If that phrase doesn't sound familiar to you, you probably don't spend a lot of time in Icecrown. TFA stands for Threat From Above, a daily quest given out by the guys from the Argent Tournament once you reach champion level and defeat the Black Knight.
When I first found out about this quest I thought that it was a bit stupid. A daily group quest? Aren't normal group quests annoying enough? Who'd want to do them every day?
However, I soon had to realise that the reason group quests are usually annoying isn't because they require a group, but simply because considering the sheer amount of quests in Azeroth and the fact that many of them consist of long chains, it can be hard to find someone who is online at the same time as you, not doing anything else and just happens to be on the same quest as you.
Now a daily group quest with good rewards, that's something else! People can and will do it over and over again, every day, for weeks and months. I don't know how it is on other servers, but on Earthen Ring groups just for this quest are forming in general chat roughly every five to ten minutes, unless you're online at a particularly quiet time.
In many ways, it's a pugger's dream. Not only are there groups available to join at any time, but group composition doesn't really matter. You need a group, but you can team up with anyone. A tank and a healer can easily take down Chillmaw on their own, if slowly. However since he doesn't hit very hard, a dpser (even in cloth) can tank him just as well with a dedicated healer. A tank with a good dps at his side should be able to survive long enough to kill him even without healing. And a group of nothing but dps can just nuke him down really quickly.
Basically you get all the good points of a pug without the downsides. You can meet a lot of different people, but since the quest is so easy you don't have to worry if they play terribly or act like jerks, you don't have to hang around. Annoying druid trying to kill-steal the bombadiers from the group in front of you? Make note to avoid him in the future. Nice rogue offering to help the healer with the scourge killing daily afterwards? A good addition to your friends list.
I really have to hand it to Blizzard, implementing a quest like this was a great idea. If you're a player who runs solo a lot of the time but would like to meet other nice players without risking too much frustration, joining for "TFA" is simply an opportunity unlike any other.