What does M mean?

At the festival people were whispering about whether anyone still had M.

Dutch student slang. This is a Dutch word. You will hear it a lot at Dutch universities, student associations and in student houses.

The letter is mostly used around parties and festivals as a short way to say MDMA. In English you might hear molly. Pills of the same stuff are called X. If you ever use, know that drug testing services exist in the Netherlands. Safety first.