What does イン mean?
イン is a Japanese noun meaning “in (of a ball; in tennis, etc.); inside the line” in English. It can also be translated as “enter here, back nine, inside lane (track cycling, speed skating, etc.)” depending on context. It is written as イン in hiragana, and in in romaji. This word is part of JLPT N3 vocabulary.
Example sentence
打球がインかアウトかを判定するのは難しいことが多い。
It is often difficult to see if a ball is in or out.