What is a fermata and how does it work?

Adding on the previous answer, yes, fermata is when a note is held longer than the sheet music says.

It may not necessarily be in singing, but also any instrument, whether it can "hold" a sound or not. For example, a guitar string may no longer ring, but the note is technically "held".

Usually, you look at the conductor to gesture how long to hold the note until muting.

It looks like Ω with a dot in the centre.

A pause / a note held longer than listed

Explanation:

You use it when singing usually to hold out the note past how long the sheet music says