When people use the word "it's" when the word "its" should be there. And vice versa.

"Its" and "It's" are both words, believe it or not.

Example for "It's":

It is alive = It's Alive

It is alive =/= Its Alive

Example for "Its":

The keyboard had a target.

Its target moved. =/= It's target moved. (which would be 'It is target moved', which makes no sense)

"It's chair is comfortable" is incorrect. The correct form would be "Its chair is comfortable."

I hope people understand what I am trying to say.