It means the posts you see in your home feed are in a chronological order.
You might remember back in the days (years ago), you would see the latest posts in your home feed.
If someone posted just a few seconds ago, you would see their posts on top of your home feed.
The more you scrolled down, the older the posts were.
But Instagram changed this in 2016.
They introduced the “Instagram Algorithm”. It would rank the posts in your Home Feed based on what you would be the most interested about.
A lot of people got angry and wanted the chronological order back.
It’s 2022, and Instagram brought it back.