What does in stand for?

"In" doesn't stand for anything, as it's a preposition. Prepositions are words that show the relationship between a noun or pronoun and other words in a sentence.

Here are some examples of how "in" is used:

* Location: "The cat is in the box."

* Time: "I'll be there in an hour."

* State: "He's in trouble."

If you're thinking of a specific acronym or abbreviation, please let me know!