lsmod is a utility which lists currently loaded modules.
A Linux kernel can have modules for drivers or other functionality. To keep the size of the kernel small, the modules will be loaded only when specified and as opposed to built in modules will not bloat the kernel if e.g. the driver modules hardware isn't present.
This program has only two possible arguments: -V (--version) and -h (--help). Their use should be self-explanatory.