The definition of a teaser trailer

A teaser trailer is a sequence of short moving images put together to advertise an upcoming media product, such as a film, video game or television programme. It is usually between 30 and 90 seconds, which is relatively shorter than a theatrical trailer. Containing little, if any footage from the actual film, it doesn't target to reveal the plot. They're normally released a long time before the media product comes out, hence the term 'teaser'.