What is the definition of ultimatums?

Answer 1

An ultimatum is a condition you may put onto a particular thing by you for somebody else such as you may say to someone that you live with that you are giving them an ultimatum which is either to continue doing whats clearly causing you some distress or you will leave them or throw them out so an ultimatum is a way of saying it is my way or the highway or if you dont do this then i will do this or that they must change or stop doing something or else.

Answer 2

It is a demand accompanied by a threat, in which there is no room for bargaining or negotiation. Unless the demand is fully complied with, the threat will be carried out. The word is related to "ultimate" which means "last", and so means that this is the last chance to comply with the demand and avoid the threatened action.