The World is the name of the Stand of DIO but, this was back when the Stands were almost exclusively name for tarot cards. But after a while, the stands assumed a new naming convention. Despite this, when it finally reappeared in Steel Ball Run, it still maintained the same name despite the 7th Part having little to nothing to do with tarot. To understand The World, we have to understand the meaning behind the card that represents it.
The World in tarot card reading can be represented of the Cycle of Life, it's systems, nature, the end of a cycle and the start of a new one. The World is the last card of the deck and once it is reached the deck immediately begins again with the first card, The Fool. That's a totally different stand to examine. If you guys like these deep dives, maybe I'll begin exploring the meaning behind every tarot stand. But anyway. The card represents the cycle and-or the end thereof. This card is indicative of the Heaven plan, and explains why DIO is the only character who can use his stand to achieve a Heaven Stand. Made in Heaven represents the cycle of life. Through the control of time, one gains control over the fate of the world and it's cycle, by speeding up time. If the cycle is completed, the world begins again at the start. If the user died or stops the ability before the cycle completes, the cycle is broken and a new timeline is created. This is the representation of The World card and the destiny of DIO. This is all well and good. But by the time that Part 7 occurs, this no longer matters, as Diego is never meant to fulfil this destiny, meaning that the name of his stand becomes a lie. For those who don't know, tarot cards are often used to determine one's future, so in Part 3, it references DIO's destiny to become integral to the cycle of the universe. But in Part 7, this doesn't work. In Part 7, Diego dies. Twice. And is no longer really used to impact the universe. Therefore, in Part 7, his stand should not be called THE WORLD. As that is not his destiny. It should follow the new way of naming stands. And what should it's name be?
Holy Diver.
We need to realize that The World's appearance in Part 7 was to reference DIO from the previous parts, with his Utaraptor form representative of his Vampire form from Part 1, and his Stand representative of his Part 3 form. But that's exactly why Holy Diver is a perfect musical reference, because this song might as well be the plot of DIO's life. Allow me to explain.
Beyond the common references in that his Stand looks like a scuba diver and is owned by a man named Dio, it has other references. Considering that The World is the only Stand capable of achieving Heaven, that fulfils the "Holy" part of the name. But if you look at the lyrics and the meaning behind the song, it makes sense.
Holy diver
You've been down too long in the midnight sea
Oh what's becomin' of me?
After the ship went down, Dio spent years under the sea, doomed to rot until he was finally pulled back up. According to Jorge Joestar, Dio used Jonathan's stand to see what was going on in the world while he waited. This means the first Stand Dio ever awakened was Hermit Purple, because that's what Jonathan awakened. That being said, the canonicity of Jorge Joestar is... not there, so take it all with a large grain of salt.
Ride the tiger
You can see his stripes but you know he's clean
Oh don't you see what I mean?
This would be a reference to Dio taking the body of Jonathan Joestar, something that would eventually bite him due to eternally linking his destiny with that if the Joestars'. This would also reference the purity of Jonathan's heart, considering him "clean".
Got shiny diamonds
Like the eyes of a cat in the black and blue
Something is coming for you, look out!
This could reference the amassing of funds and the influence of DIO across not only Egypt, but the whole world via his flesh buds and servants. Though a part of me wants to make reference to Crazy Diamond, who in English localization is called "Shining Diamond", and Josuke's stand already looks a dud amount like DIO's, who Josuke has a deep connection to due to DIO possessing Josuke's Great Grandfather's body. Josuke's ability is a perfect fusion of DIO and Jonathan, in that it's a close range power type, but is a completely selfless stand. But moving on, the Cat in the black and blue could reference the Joestars, possibly Joseph who can see DIO with the same stand that DIO uses to see Joseph. This is further supported by the idea that there's something "coming for" the Holy Diver.
Race for the morning
You can hide in the sun till you see the light
Oh we will pray it's all right.
This part is less for DIO and more for the Joestars, in that they discover how powerful DIO really is and thus flee from the one the spent nearly 50 days searching for. They knew they were at disadvantage due to the night, so they planned to race for the morning to hide in the sunlight until they could develop a strategy to kill DIO. All the while praying that they would not be killed.
Between the velvet lies
There's a truth that's hard as steel, yeah.
The vision never dies
Life's a never ending wheel.
This part is in reference to Pucci and DIO's relationship. DIO played on Pucci's heart, and led him down a path of self-righteousness, causing him to give into the concept of paving his own path to hell in good intentions. DIO lied to everyone and used his great charisma to fool everyone. But despite all of the lies he told Pucci, the one thing he was truthful about was the Heaven Plan. That was the basis of their relationship. The mutual decision to follow that plan. The giving of the bone to Pucci is referenced in the lyric "The vision never dies". This way DIO had security, knowing that even if the Joestars killed him, his plan would still be unstoppable. This leads into the lyrics "Life's a never ending wheel", which is a direct reference to Made in Heaven, who's whole ability was to cycle through eternity to spawn a new universe where everyone knew what their future was.
Say, holy diver!
You're the star of the masquerade!
No need to look so afraid.
This part I'm not entirely sure about. But if I had to guess, it either is a complete overview of JoJo's Bizarre Adventure, every part somehow dealing with something DIO was doing. Part 1 is the rise of DIO. Part 2 was the means of Dio's rise. Part 3 was the return of DIO. Part 4 was the aftermath of DIO. Part 5 was the child of DIO. Part 6 was the endgame of DIO. Without DIO, the entirety of JoJo would not have happened. This makes him the star as, despite every part following a different Joestar, DIO is the one constant. He's spoken of more than any Joestar, perhaps barring Jotaro. The next part is "No need to look so afraid", which could possibly reference his need to "have courage to destroy his stand". That being said, this entire lyrical section could be about the heaven plan, but I'll leave that to you to decide.
Jump, jump, jump on the tiger!
You can feel his heart but you know he's mean!
Some light can never be seen, yeah.
This part seems to reference Jonathan again, and how he naturally was still fighting against DIO, in that DIO even admitted that his left side regenerated slower than his right side. It could also be a reference to Jotaro who killed DIO due only to a rage boost. Jotaro has to be the meanest Joestar of them all, with his whole persona being a Yanki School Kid. The "Light that can never be seen" could be in reference to Jonathan's soul sabotaging DIO by weakening his left half that allowed Jotaro to kill DIO. It could also reference the inner strength of Jotaro that proved to be as devastating to DIO as his greatest weakness, the sun.
The lyrics of the song seem to reference the life of DIO. Considering that Ronnie Dio, the writer of the song, stated that the song is a reference to a chosen one figure who would play the part of a Messiah-esque figure who would "Die for his world", DIO would seem to match given his name and own self-image, in that he could deceive a priest into thinking he was basically a god matches this. The reference also that DIO had to die to awaken a heaven stand according to his own diary also matches this. Indeed DIO is more of an anti-Christ like figure, a twisted mockery of our Lord Jesus Christ. DIO fits very well with this song which almost makes me think that Araki had this planned from the beginning. That's why I think that Diego's stand should not have been known as THE WORLD in part 7, but as Araki likely wanted it to be called, "Holy Diver".