what is shell?

tell me differeent types of shells in unix

Bourne shell (sh)
C shell (csh)
TC shell (tcsh)
Korn shell (ksh)
Bourne Again SHell (bash)

Shell is a command line interface. means in a text based operating system.
There are 6 tyepes of shells
Born shell
Korn shell
Bash shell
Csh shell
Tcsh shell
Z shell.