Reposting this because it's relevant:
Meta is short for metagame. The pro scene has a metagame; solo queue has trends.
Especially at low levels, there really isn't a "meta", people just misunderstand the term. The "metagame" is the game outside the game, that is, involving elements that are not actually in the game, but "in your head", in a sense. Bruiser/tank top, bruiser/fighter jungle, mage mid, ADC and support bot is not a meta or "the meta". It's just the roles in the game, it's what types of champions go in what lane. What champions are popular is not "the meta", those are trends (although it's a bit closer).
The "meta" is misunderstood, and is often referred to even by knowledgeable people such as casters as "mind games".
The best way to understand what the meta is, is to imagine two people playing rock paper scissors. Both are male. Person A has heard that most males will open rock, for psychological reasons. Person B has heard this, too, and is aware that person A has heard it. In this "metagame", person A may want to open paper, anticipating a higher likelihood of rock. Person B, aware that A is aware of "rock first tendencies", will anticipate a paper opening, and will want to open scissors. If we take this a step further and make person A aware that B is aware that A is aware, person A will want to anticipate B's anticipation by opening rock, in which case he gets a draw if B opens rock (as is the tendency) and wins if B opens scissors, anticipating a paper opening to counter the expected rock. This is a metagame in action, and as you can see, even with a simple game with only three in game variables, it can get pretty in-depth, because a metagame is a game-outside-the-game that plays on variables outside the game, such as what all involved players know, tendencies, psychology, and many other things. Saying "the meta is who goes where, what champions are popular/best, how people are currently playing, etc." is a complete misunderstanding, an unfortunate one that a large majority of this community perpetuates.
If you want a better explanation of what a meta is and looks like, I can describe it very well by comparing League to Starcraft, which obviously doesn't have "roles" or "champions", but, being an RTS, has a very active and dynamic metagame. I've already written a lot and this is a personal peeve of mine, so I won't go into it unless someone asks me to do so in order to further clear up this frustratingly common misconception.