[andrewas]

Third party mods are modifications made by persons other than the creatores. Purely optional, and generaly a bad idea on your first run though. Some make the game easier (ease of use), many make it harder (tactics), some expand the storyline (ascension, The Darkest Day), some add new NPCs (theres a whole thread of those on the SoA forum) and some add bugs (The Darkest Day especialy).