Every language use different 'registers' depending on the situation, the people involved, if it is written or spoken....
You can have a formal register (could you, would, if you please, dear sir....), informal register (please, can you, call me...), professional register e.g for a doctor (stetoscope, patient's notes, prescription)...
For example, if I go to the doctor and tell him 'my tummy hurts' I am using a child register which is not appropriate to the situation, same again if my students great me with 'alright darling', it is not the register I expect them to use to speak to me.