A schedule poster is one image that maps out what a label plans to post between the announcement and the release. It usually comes as a calendar grid or a dated list, and you may also see it called a promotion calendar, a promotion schedule or a comeback schedule. Typical entries are concept photos, a tracklist, a highlight medley, music video teasers, and then the release itself. They are labelled but not explained, so what you read is a run of date plus item.
You can meet the poster in two forms. One is a still image on the label's other channels. The other is a short video on the official video channel, and that version is the reason it turns up in a feed of uploads next to everything else. It can look like a teaser at a glance, but the difference is simple: a teaser gives you a piece of the content, while a schedule poster carries only dates and labels, with no footage from the release.
Here is why it helps. It is a single place where the whole run of dates appears together, so you can tell how long the promotion lasts and when the release lands, instead of learning each step on the day it happens. If you plan your time around a release, that overview lets you line things up in advance, and it gives you the shape of the whole run in one look.
Now the part we want to be direct about. The dates live inside the image. If you read only the text description under the upload, you may get the release date and little else, and sometimes not even that. Automatic tools and feeds do not read the grid, so a schedule poster is a case where you have to look at the picture yourself. Keep in mind that the posted schedule can shift too. Labels do move or add dates, so treat the poster as the plan as it stood on the day it went up rather than a guarantee.