A titan is a person who is huge in their field — huge in power, in achievement, or in influence, not in body size. A titan of industry owns half a market. A titan of literature is a writer everyone else measures themselves against. The word carries respect, sometimes a little fear, because a titan is big enough that other people have to work around them. It is a written word more than a spoken one: newspapers, obituaries, business magazines, book reviews. You would not say it about your friend at lunch. You can also use it for companies and organisations — "the tech titans" means the giant firms. Written with a small t it is this everyday meaning; written with a capital T, a Titan is one of the original giant gods of Greek myth, and that is where the meaning came from. Because the Greek Titans lost their war against Zeus, the word sometimes keeps a faint shadow with it: enormous, and not guaranteed to last. Most of the time, though, English uses it as straight praise for scale.