what exactly is jamming?

[ChrundleTheGreat]

im working on a scenario that is meant to be similar to the one in liberty where you have to move through the map without being detected, exept i wanted terrain such as hills and mountains to block the enemies vision, i sort of heard that jamming was related to blocking vision, but i dont really know how it works or if it has anything to do with what im looking for, i had also thougth maybe vision points can be modified and i could give them a terrain based cost same way movement points have, but im still curious as to what jamming does.
i hope some of you can clear this out for me.
thanks a lot
--Chrundle

[Ravana]

https://wiki.wesnoth.org/UnitsWML#.5Bmovetype.5D [vision_costs]

[dwarftough]

Your task should definitely be about [vision_costs] but if you wonder what is jamming, viewtopic.php?f=21&t=44577&p=644985#p644985 (the link was on the wiki page, yeah). It's about a unit impeding vision for its enemies around the place it stands