A pocket guide is what we used to call in grade school a cheat sheet. It contains vital information to allow you to pass a test—or, in the case of a physician, to recognize and have detailed information about a disease you might not otherwise think about. Usually the data are complex; otherwise, they would be easy to memorize and would not require the use of a pocket guide. It stands to reason that the pocket guide must contain sufficient information to allow a diagnosis to be made and to cover the basics of the disease and its therapy, but at the same time it must be small enough to fit into a pocket.
Elgart ML. The Pocket Guide to Fungal Infection. Arch Dermatol. 2001;137(3):389-390. doi: