A sprint is a time when programmers come together to work on interesting projects. It is usually a daylong or multi-day session. Sprints have been very successful at Python conferences. Sometimes the main developers of a package will add features, squash bugs, or do design work (that's a euphemism for a lot of talking). Other times the focus is on learning to use a library by building a program (e.g., a game). Sprints also provide a time for lightning talks (short 5-minute presentations on any Python topic) and other stuff.
SeaPIG has hosted two Python sprints so far. Reports on them and planning for future sprints is on the NorthwestPythonSprint page.