(~s)
1.
The ~ to a book or talk is the part that comes at the beginning and tells you what the rest of the book or talk is about.
Ellen Malos, in her ~ to ‘The Politics of Housework’, provides a summary of the debates.
N-COUNT: oft N to n
2.
If you refer to a book as an ~ to a particular subject, you mean that it explains the basic facts about that subject.
On balance, the book is a friendly, down-to-earth ~ to physics.
N-COUNT: usu N to n, oft in names
3.
see also introduce