Some first order languages include function symbols as well as names and predicates.
Function symbols allow us to form name-like terms from names and other name-like terms.
We can do this in English with phrases like
Max
Max's father
Max's father's wife
Max's father's wife's husband
The sum of 3 and 4
and in FOL with ``terms" composed of a function symbol followed by an appropriate number of arguments
Max
father(Max)
wife(father(Max))
husband(wife(father(Max)))
sum(3,4) or 3+4