It's is defined as a contraction of it is or it has.
An example of it's is what you write when a friend asks you how a new job is and you want to give an informal response - "It's great." as opposed to a more formal response "It is great."
- it is
- it has
- Contraction of it is.
- Contraction of it has. See Usage Note at its.
- See Usage under “its”
- (now nonstandard) Alternative form of its.
From it + ’s.