A book of contact details
(names, address, telephone number
s etc). Usually a small, black, leather covered book
carried by a gentleman
. Gentlemen with very large social circles
may also maintain a rolodex
of contacts with whom they correspond with less often.
In classic detective movies the detective goes through a murder victims little black book to determine their associates.
Both little black books, rolodexes and classic detective movies have now been replaced by electronic databases and crappy hollywood movies.