# Basic Knowledge: Variables

Variables are specialised → terms to store information during runtime. They can be used to define → literals with a placeholder and (in contrast to → atoms or literals) begin with an upper-case letter.

There are two kinds of variables

• the garbage bin variable _, which can be used as a substitute in cases where the content of the variable is not of interest, but a variable has to be provided.
time( current( hour( Hour ), minute( Minute ), period( Period ) ) )
Note: The upper-case variables Hour, Minute and Period can be assigned to values automatically. This mechanism is called → unification.