What is the letter ƒ in mathematics?

The letter f usually indicates that the equation is a function in the notation f (x).

Example: f (x) = x + 1

It is a fancier/more proper replacement for the variable 'y'. The same is used for the letter g as in g (x) and h as in h (x).

OR

It could just be a regular ole variable

Example: f + 1 = 7, solve for f