bash is GNU Bourne-Again SHell. Bash is created by the Free Software Foundation, Inc. From the man page:
Bash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. Bash also incorporates useful features from the Korn and C shells (ksh and csh). Bash is intended to be a conformant implementation of the Shell and Utilities portion of the IEEE POSIX specification (IEEE Standard 1003.1). Bash can be configured to be POSIX conformant by default.
Type the following command at your terminal to read more about bash: