A lookbook is a collection of photographs compiled to show off a model, a photographer, a style, or stylist or a clothing line. Usually, bloggers or vloggers will "model" fashionable looks for that month or season. This gives viewers ideas on how to style outfits, or to show what the latest fashions are. It is an especially popular term with "fashion bloggers".
Lookbooks in their online form can be described as "fashion diaries" because bloggers are constantly updating them on a daily or weekly basis. However, sometimes they are made to compile the looks of other people such as a celebrity, politician or socialite. They can also be used as an artist's portfolio.