To express your desired intention to the assistant you can use natural language. In this context, ‘natural’ means that a user doesn’t have to say specific pre-programmed commands/words/expressions to trigger a specific action, but can rather speak naturally, as they would to a fellow human being. For instance, if you wanted to know the weather for Paris, you wouldn’t need to say “Weather Paris today 20:00h”. Instead you could say “I’m going out tonight, do you think I’ll need an umbrella?”. The NLU is the mechanism in charge of deriving the meaning or intention of the command independently of the way it is being expressed.