An artbook is a book full of art.  Generally wider, taller, and on nicer paper than boring old [i]textual[/i] books, an artbook has many pieces with some unifying theme (like "all produced for a particular [[animu|Chinese cartoon]]" or "all by this one person and/or the team of computers imitating them after they died") collected in one convenient consumption-ready package.

Artbooks also sometimes have design notes, previously unreleased sketches, demo drawings that didn't make it, etc., so they're sometimes interesting to fans in also showing what could have been and/or wasn't.