Farming is when you stop playing the parts of the game you want so you can spend time collecting materials/glimmer or other things to succeed. Example: "I finally completed the Thorn bounty, but I have to grind some bounties and farm some mats so I can upgrade it fully before it is useful."

Weeeelp........ it is the simple act of remaining within an area, with the knowledge of how enemies respawn as you cultivate the bad guys while reaping the rewards of their painful suffering and DEATH at you hands. Mmmhmm, I recon you'll do just fine.

farming is the means to stay in one area or killing any group/specific enimies and reape the rewards. this happens in any loot generating game. wow. borderlands. diabol 3. and so on :)

OK... Farming materials: go to a planet patrol zone and just collect all the materials (spinmetal, spirit bloom, relic iron, or helium) you can find there. Also hit all the loot chests you can find for the same materials. This builds your stock of upgrade materials. Farming glimmer: usually also done on patrol, but can happen during a strike; pick an enemy type common to the area you're in, and activate a glimmer boost item. Example: on the Moon, Fallen are the main enemy- so use an Ether Seed, then go hunt Fallen. Every one you kill adds glimmer to your bank. Repeat every 10 minutes as desired until you're tired of patrolling or until you have enough glimmer. Farming engrams: every time you get a kill, there's a chance your enemy will drop an engram. Head shots seem to increase this chance. This goes hand-in-hand with glimmer farming, since they both involve killing things. There you have it; "farming" is just the process of accumulating materials, money, or items in the game. You're most likely doing it already. Enjoy.

Killing Enemies and Doing Missions for a certain weapon, material, engram, etc...

Doing the same thing over and over for certain materials

Simple way Killing the same enemies over and over again for loot. :D