Support is a mindset, not a pick. That's where, for starters.
Off-meta is often treated like an unsung hero but usually, people see some dumb shit in a youtube video, go, "OH I CAN DO THAT" without considering what might go into the planning or execution (IE five-man premade), and they then proceed to shit up a game and tell others they're just being jerks and meta slaves.
A support is putting their ally's kills and health first, keeping the rest of the team as abreast of as much information as they can, and contributes to teamfights by using the enemy or ally formation(s) to their advantage. If it were as much as heals, it would exclude Brand (and doesn't, really); if it were just CC it would exclude others (and doesn't). Realistically, it's more of the role you're taking on. You could play a Darius support, probably; and quite well in the right circumstances, you'd just have to know what you were and weren't working with.
To me, a support is a player, who in layman's terms ensures the rest of the team achieves the glory-- usually at cost to themselves. You need to realize why you're buying Sightstone instead of Sheen; you need to realize why you have an income item instead of a damage starter. You need to understand when you're using which +Heal item. You need to know when you're blowing big cooldowns, and when you're just trying some small peel or sustain. It's about knowing why you're in the lane at any given time, which is to make the carry look good. Even when they're looking badly and dragging you down, it's your job to pick them back up and get them upright. That's why mage picks made it hot for a while-- because even with a carry who's behind, they can take up the mantle. They can equally fall back if that ADC picks up. Enchanters (to a lesser extent, tanks as well) can't do this because to most of them, 'ahead' equates to 'roughly with everyone else, damage-wise.'
A support is a player who knows when and where they're needed, and they don't need a reason for it. All vision, all the time; ask players if they have any hot spots they want warded. Communicate with your lanes to know who is, and is going, where. Critically, realize that you are meant to be less valuable than the rest of the team; part of this is so that as a weaker individual part, you're also a weaker individual loss. You can turn this to your advantage in martyr plays when necessary, by letting player(s) 'secure' a kill that gets them killed, or pushed. Of course, try not to die just to get one kill... this-for-that is rarely worth it in League.