From the Glossary:
Points of Issue: Points are physical attributes that are specific to a printing or edition of a book, such as a typo on a specific page that was corrected in later printings of a book.
An issue of a book is a specific change in the book during the printing of an edition. A first edition of a book may sometimes have two or more issues, which would be defined by a change or correction in the text, binding style, or any other physical feature of the book during the first edition printing.
Typically, the first issue of a first printing would be the most desirable copy for a book collector.