In computer software, a Module means an optional piece of code that isn't required for a program to run, but can be loaded when needed.
When talking about the Linux Kernel, it means a Driver or other piece of code that the kernel can load and use on request. Examples include DeviceDrivers for various pieces of hardware that aren't required for the computer to boot and work (such as sound card or graphics card drivers), and modules for various network protocols and disk formats that might not be used very often, so don't need to be loaded in memory all the time (such as the ISO-9660 disk format used by CDROMs, or the PPP or IPv6 network protocols).
modprobe -r modulename
NB You cannot always remove a module, especially if in use or module removing has not been compiled into the Kernel
There are a number of options you can alter for modules you can alter when building the kernel under "Loadable Modules Support" that may be use for you if you are Kernel developer.
to see the list of supported options for a particular module.
options ov51x led2=0
where the above example sets the led2 option to 0 for the ov51x module.
On a 2.4 series kernel, these settings go into /etc/modules.conf instead. (On Debian-based systems using a 2.4 kernel, put your settings into a file in the /etc/modutils/ directory and then run update-modules to re-create the modules.conf file.)
Regardless of which kernel you are running, you will need to unload and then load the module for new parameters to take effect.