clear a variable

Hello,
    I can't seem to find this in the documentation, is there a way to clear a variable.  For example I have an application that opens displays a bunch of images, they can be big memory hogs. When I'm not showing them I'd like to clear out those variables, instead of having to close down my program and start over.  I know matlab has a command "clear var" which will do exactly that.
    Thanks for the help!
       Andrew