Some commands expect you to enter additional data from the keyboard after you have pressed Enter. In such cases the cursor is positioned at the start of the next line and either no prompt appears at all or a special prompt, varying according to the command, appears instead. Each of the lines you now enter must be terminated with Enter. To terminate data input, you generally either press CTRL+D (or use @@d at block-mode terminals) or enter one of the special statements associated with your command.
If you terminate a command with Enter leaving the command line incomplete, or if you escape Enter with a backslash (\), the POSIX shell outputs the value of the shell variable PS2 as prompt. By default this is the "greater than" character and a blank ('> ').