A 'pull quote' is a large quote in a newspaper article or suchlike, designed to 'pull' people into reading the article. They typically contain lurid extracts of the article, that make it seem interesting and readable.
For example, in The Mail on Sunday's 'Review', the Page 48 article has a pull quote: "Tanks turned their guns on my car".
It is hard to illustrate this better within e2's HTML filtering, so it's probably best you get a newspaper or magazine and look for yourself.