The name Prolog stands for "predicate logic." The language is designed to look a lot like logic, with axioms and rules. It may look a little odd if you've never seen it before, but it's a complete language, just like Java. In theory, any program written in Java can be reproduced in Prolog.
Prolog is a rule-based language. You define your rules, then you ask a question. The Prolog system uses the rules to find out the answers to your questions.
Prolog is often used in natural language processing, planning, and computer vision applications. Languages like Prolog are becoming increasingly popular in the field of knowledge representation and particularly for agent-oriented programming.