Yes, it is mainly for *nix nerds. bash and the others listed are command line interperters. When you type in commands via ssh or telnet, a program this program takes it and tells your hardware what and how to do (through low-level programming language).
The differences between the 4 interperters dreamhost has are relativly small. All the commnds work the same, just syntax changes.
That's probably more than you ever wanted to know.
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