Talk is a program to allow two users on two different machines to talk to one another in real time.
To use talk you first need to know where someone is logged into. For this example we will say that your are user edward who is logged into the machine tea.eng.umd.edu and you want to talk to your girlfriend mary who is logged into picard.src.umd.edu and has username mary. The following message would then appear on her screen telling her that you want to talk to her. This will establish a connection between the terminal screens. The screen in which you gave the command will split in two and the top screen will show what you type and the bottom will show what the other person types.