Same as post or posting as a message or a commentary posted on an internet forum. Poast instead of post follows the same pattern of transcribing "ou" diphthong as "oa" as in moar instead of more.

In the realm of interwebs, there are posts and there are poasts. A post can only become a poast once it has reached the relative hotness of toast. In other words, if it is popular.

A post someone makes on social media to deliberately boast about something which has happened to them.

Boastful post that make the poster feel better about themselves, but for whom other can't care less.