This is the noun version of the kanji mistake, so it means a mistake or if it's on a computer, an error.

Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:

When you make a mistake, you need to admit to it. When someone asks, "Who's responsible for this mistake?" You say, "I am (あやま)."