It's a preposition that can mean:
* Into: "He walked in the house." (Latin: "Ambulavit in domum")
* At: "She was in the garden." (Latin: "Erat in horto")
* During: "It happened in the night." (Latin: "Accidit in nocte")
* Among: "He is in the crowd." (Latin: "Est in turba")
It can also be combined with other prefixes to create new prepositions:
* "in" + "ter" = "inter" (between)
* "in" + "tra" = "intra" (within)
* "in" + "super" = "insuper" (upon, besides)
Therefore, "in" is a very versatile word in Latin and can be used in various contexts with slightly different meanings.