I like what you're doing here, but I've got something to add. Particularly about this sentence.
Originally Posted by Niek
A support is a champion whose sole goal is to make sure their laning partner gets fed.
While the general idea is a good one, this is a really lackluster definition of a support. A great deal of players have at one time or another taken this definition at face value, pretty much exactly as you said it here; I did it too. It's an idea that I've seen lead to a great deal of awful support play, bad ADC attitude, and poor teamwork all around. A more accurate definition might be:
A support is someone who makes their teammates stronger, primarily by substantiating the ADC.
ADCs are known for their devastating damage, kiting, and siege potential late game. However, in exchange for their range and excellent attack damage scaling, they make tremendous sacrifice to base stats. This is one of the biggest reasons supports exist. A good support knows that it is his job to make up for the missing attack damage, attack speed, health, resistances, and/or crowd-control of his lane partner for as long as he needs it.
Supports worth their salt will make every effort to ensure that their ADC gets fed, but if they cannot accomplish that, they are not necessarily bad supports. If all they are able to do is provide zone presence enough that their ADC can last hit under tower, they are not doing it wrong. Good supports know that as long as their ADC continues to accumulate gold and levels comparable to their counterpart on the opposite team they will eventually become very dangerous in their own right!
Great supports understand that the game doesn't end at their laning partner. If bot lane is lost, the game is not. If the ADC is 23/0/0 their job is not done. A good team shouldn't amount to just the sum of it's parts, and a great support will ensure it's more than that. With wards, timers, auras, CC, etc. supports do their best to make up for anything their teammates can't do, won't do, or haven't thought of.
Supports aren't just a fifth wheel mandated to 0 CS by the economics of Summoner's Rift, or simple babysitters. I just thought you might want your first sentence about them to reflect that.