What is meta?

everyone is talking abot this is the meta now, meta champs, that champion dosnt fit the meta etc what is meta actually? can someone explain. Ive been flamed because i dont play meta champs top, that are my main role. but iam doing fine anyway top lane. 70 games iam in promo to silver 3, started bronze 5, gonna head to gold and see what the life gives me. But anyway, what is this meta thingy, and why do ppl flame me because i dont play meta champs?
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