Informed consent is consent that is given freely and willingly by someone who is aware of what they are agreeing to, not under the influence of drugs or alcohol, not being pressured or coerced, and of legal age. Informed consent is often referenced in BDSM communities. It is vital before starting a scene, especially any scenes that involves play that appears nonconsentual such as forced orgasm.
More About Informed Consent
It could be said that anything other than informed consent is not true consent because the consenting party is either not actually able to give consent (as is the case with children or the intoxicated), is unaware of what they have agreed to, or is agreeing under duress. Consent must be given freely and with awareness.