This is an alias which calls to ChanServ. It reduces your amount of typing. Instead of always typing /msg chanserv <command|rooml> [parameters], you simply type /cs <command|room> [parameters].
Example:
/cs set #conferenceroom mlock +tn
Most clients will understand /cs, but if you are using one that does not try:
/quote cs <command>
/chanserv also works as an alias, and also may need a quote, depending on the program you use.