PostEaseThe short answer
A teaser post reveals part of an upcoming announcement, product, or piece of content while deliberately withholding the full detail, in order to build anticipation ahead of a full reveal. It is a common part of a launch build-up sequence, used before the actual announcement goes out.
It only works when the reveal delivers
A teaser builds anticipation only if what eventually gets revealed is worth the wait. A teaser followed by an underwhelming reveal damages trust more than announcing directly, with no teaser at all, would have.
A specific detail teases better than a vague hint
A teaser that reveals one interesting detail, a particular feature or a date or a real image, generates more anticipation than a vague "something big is coming" post with nothing concrete attached.