In the film industry, the term ‘slate’ can refer to one of two things:
1) Clapper Board
Slate is another word for clapper board. In this context, it originates from the early days of filmmaking when scene and take information was written onto an area of the clapper with chalk. At the time, slate was a preferred material for black boards.
These days, ‘slate’ is also used to refer to an instance of the clapper board when it is shown on screen. Normally, the clapper is shown at the beginning of the take, prior to the action commencing. This is a standard slate. In situations where it is easier to show the clapper at the end, this is known as a ‘tail slate’. An upside down, open clapper is used to denote a take in which sync sound was not recorded. This is called a ‘mute slate’.
2) A Collection of Projects
Producers and production companies are often referred to as having ‘a slate’. In this context, it is simply another way of referring to a group of projects. A company may go to a festival or market with it’s slate of completed films, or it may also have a ‘development slate’, a group of films that have not been made yet.