The easiest way to explain what the mods were is to watch the film Quadrophenia 1960s Mods & Rockers film
mods, mods, mods
moddb.com is good for mods. It has mount and blade mods and mods for virtually every other game.
you can get minecraft mods and textures off the minecraft mods website.
The Mods was created in 1964.
you can easily get mods from planetminecraft
look what ever game you want and add the word mods to the end on google. e.g oblivion mods, GTA mods
All mods are 'legal'.
Marvel mods
That depends on what mods you're talking about.
Get all the mods!
You can't get mods on the Xbox 360 because it can't download mods at all.
Mods, or add-ons, are modifications to the game.