A demand (/dəˈmænd/) is a forceful claim for something, a requirement, an urgent request or an an order. In English it can be used as both a noun and a verb.
A demand can also be formed by using an imperative. It can also be expressed using modal verbs, e.g. "You must..." or "Will you..?"
As a verb, demand is a regular verb, with the forms demands, demanded, demanding, etc. It can introduce a relative clause, e.g. "He demanded that I help him", or it can concatenate with a to-infinitive, e.g. "I demand to see the manager!"
Demand is a false friend with its French cognate demander. In French, demander means to ask, and demand is better translated as exiger. This is because the Norman French who brought this word into English had higher social status than the local English peasants, so for them to ask for something was effectively a demand.