Hey, a cvar is something like a persistent variable (till server restart). It can only contain strings, integers (int) or floating point numbers (float).

In server-console you can do:
set somevalue HELLO
somevalue -> will print HELLO

Then there are some codscript-functions to access those variables:

Code:
gethello = getcvar("somevalue"); // the variable gethello contains HELLO now
Code:
setcvar("somevalue", "BYE"); // the variable gethello is set to BYE now
What returns this function-call now? getcvar("somevalue"); *question for you*


Like the server got cvar's, a client got them also. You can set client-cvars like this:

Code:
player setclientcvar("com_maxfps", "125"); // everybody can strafe now :D