The four books refer to The Analects of Confucius, Mencius, University and The Doctrine of the Mean.
The Five Classics refer to The Book of Songs, Shangshu, Book of Rites, Zhouyi and Chunqiu, which are referred to as "Poems, Books, Rites, Changes and Chunqiu" for short. Before this, there was a book "Yue Ji", which was collectively called "Poems, Books, Rites, Music, Change, Spring and Autumn", and these six books were also called "Six Books".