Usain Bolt is fast at running. He says on the BBC, 'I think I'm one of the greats, definitely,' but his 'personal goal' is to be a 'legend', and this means he needs to defend some titles. 'People have crowned me a legend already,' he says. 'I haven't really placed myself that high yet.' I like the idea of 'legend' being a technical, definable term, because:
a) it sounds so ridiculous.
b) it absolutely is. There are rules surrounding the designation - different rules in different contexts - and Bolt knows that. He knows that 'legend' is better than 'great' and that's what he wants.*
As it happens, I think he's probably a legend already, but he's not definitely one, and if he never re-achieved he'd only be a minor sort of legend when he really could be Hercules.
* I've been interested in this since university. 'Legend' was casual and not particularly awesome honorific awarded to lots of those who hung around for longer than three years, since once you'd done that, you had existed in what amounted to a kind of student pre-history. Time is absolutely part of the technical definition. See also, 'icon'; 'national treasure'.