Teasers are sometimes displayed associated with links to the page, they are not displayed on the page.

A teaser may be the same as the summary. Separating the teaser and summary increases flexibility,

Along with the title, teasers help users quickly understand whether the page has the information they want.

Aim for a maximum of 160 characters. 

Teasers end with a full stop.

Teasers are information not already provided by the title