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

Precisely the lower bound or $\omega $ bfon f(n) means the set of functions which are asymptotically less or equal to f(n) i.e U g(n)≤ cf(n) $\for all $`un≥ n' For some c, n' $\in $ $\Bbb{N}$

And the upper bound or $\mathit{O}$ on f(n) means the set of functions which are assymptotically greater or equal to f(n) which mathematically tells,

$ g(n)\ge cf(n) \for all n\ge n' $ , for some c,n' $\in $ $\Bbb{N}$.

Now the $\Theta $ is the intersection of the above written two

$\theta $

Like if a algorithm is like " exactly $\Omega\left( f(n)\ right$ " then it's better to say it's $\Theta\left(f(n)\right)$ .

Or , we can say also that it give us the actual speed where $ \omega $ gives us the lowest limit.