받침 is the final consonant at the bottom of a Korean syllable block. This drill teaches you to recognise it, apply the seven-sound neutralisation rule that decides how it is actually pronounced, and handle 연음 — the liaison that carries it into the next syllable.
It is why 읽어요 does not sound the way it is spelled, and once it clicks, Korean pronunciation stops surprising you.
Every card has a temperature. Get it right and its chance of coming back halves; miss it and it doubles. K2 picks the next card at random, weighted by that chance, so a session keeps returning to whatever you are getting wrong and lets what you know fade into the background.
When the cards you are working on have cooled, a new batch joins them, so you always study at the edge of what you know. There are no review dates and no daily queue to fall behind on. Every drill is free and works without an account, and everyone gets 20 free AI uses a day; past them, signed-in AI practice runs on your Bike4Mind credits.