I am not sure what the word is, because I forgot it, but I think for this question there might be several answers, and it depends on the context, there's the word that defines the crime of lying in court (like defamation), and I think there's the act of it, which may not be a crime depending on the context, but I might be wrong. Anyway, just help me remember the word, or just answer the question broadly without considering what I wrote above.
The act of intentionally giving false information under oath is called perjury. Merriam Webster:
the voluntary violation of an oath or vow either by swearing to what is untrue or by omission to do what has been promised under oath : false swearing
And the verb form is perjure. Oxford Dictionaries:
willfully tell an untruth when giving evidence to a court; commit perjury.
Someone who commits perjury is called a perjurer.