NAMEhelp - Display helpful information about builtin commands
help [-dms] [pattern]
Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise help for all the builtins and shell control structures is printed.
-d Display a short description of each pattern
-m Display the description of each pattern in a manpage-like format
-s Display only a short usage synopsis for each pattern
The return status is 0 unless no command matches pattern.
This is extracted from the main bash man page, see there for more details.