A lie is the deliberate fabrication or misrepresentation of the truth.
Lie by Omission
A lie by omission is a statement in which everything that is said may be factually true, but that is still deceptive because material information is omitted. For example, if a murderer who stabbed his victim denies his crime by saying he "did not shoot the victim", then this is technically truthful, because he stabbed the victim. However, it implies that he did not kill the victim, which is untrue.
Lying in Religion
Lying in Buddhism
In Buddhist morality, the Five Precepts, which are required to receive as a formal oath or vow in order to be a Buddhist (unlike many liberals who call themselves Buddhists while ignoring morality), specifically forbid lying in the Fourth Precept which also forbids gossip or "divisive speech", lewd or lascivious speech (profanity) and harsh speech.