Prolog is based on First Order Predicate Logic ---sometimes abbreviated to FOPL.
First order predicate logic implies the existence of a set of predicate symbols along with a set of connectives.
First order predicate logic implies that there is no means provided for ``talking about'' the predicates themselves.
Prolog is based on FOPL but uses a restricted version of the clausal form. Clausal form is a particular way of writing the propositions of FOPL. The restriction is known as Horn clause form.
Prolog is a so-called logic programming language. Strictly, it is not the only one but most such languages are its descendents.
We will spend a little time outlining the basic ideas underlying both propositional and predicate logic. It is not the intention to use Prolog as a vehicle to teach logic but some appreciation of the issues is invaluable.