A screenplay, or script, is a written work by screenwriters for a film, television program, or video game. These screenplays can be original works or adaptations from existing pieces of writing. In them, the movement, actions, expression and dialogues of the characters are also narrated. The major components are action (sometimes called "screen direction") and dialogue. The action is written in the present tense and is limited to what can be heard or seen by the audience, for example descriptions of settings, character movements, or sound effects. The dialogue is the words the characters speak, and is written in a center column. Unique to the screenplay (as opposed to a stage play) is the use of slug lines. A slug line, also called a master scene heading, occurs at the start of each scene and typically contains 3 pieces of information: whether the scene is set inside (interior/INT.) or outside (exterior/EXT.), the specific location, and the time of day. Each slug line begins a new scene. In a "shooting script" the slug lines are numbered consecutively for ease of reference.