You may receive an email from a friend who has your email address saved in their contacts list. Your friend will say that they are in foreign country and they have been mugged or they have lost their baggage containing their money and belongings. The friend will then ask you to send them money to help them get home.
The email is a scam and your friend's email account has been hacked. It is the scammer who has sent you the email pretending to be your friend. The scammer will ask you to send the money by some untraceable method such as Western Union or Bid Cash.