青い (aoi) means "blue." Similar to 赤い, it's an i-adjective used to describe things that are blue, like the sky or the ocean. You might say 「青い空」 (aoi sora) for "blue sky." Note it can sometimes mean green for plants/traffic lights.

青い (あおい) は「blue」を意味します。空や海の色を表すい形容詞です。例：「青い空」は「blue sky」です。