What is the difference between lower bound and tight bound?

Question

With the reference of this answer, what is Theta (tight bound)?

Omega is lower bound, quite understood, the minimum time an algorithm may take. And we know Big-O is

Answer 1

If you have something that's O(f(n)) that means there's are k, g(n) such that f(n) ≤ k g(n).

If you have something that's Ω(f(n)) that means there's are k, g(n) such that f(n) ≥ k g(n).

And if you have a something with O(f(n)) and Ω(f(n)), then it's Θ(f(n).

The Wikipedia article is decent, if a little dense.