O.k. I have a question in which I am given that a function is 'defined' on an interval [a,b], for $\displaystyle a,b \in \mathbb{R}$

I tried to look for the exact definition of what it means for a function to be 'defined' on an interval but I couldn't find it.

Can it be assumed that the function is bounded if we are given that it is 'defined', and what is the exact definition of a function be 'defined' on an interval?