What is the full form of post?

That is a good question. The word 'post' is not a short form for something. It is a full word by itself. It does not have a full form like an acronym.

But, the word 'post' can mean many different things. For example, here in Canada, we have Canada Post for our mail service. A message you write on a forum like this one is also called a post. It can also be a job position, like a person has a post at a company. And sometimes it means a big piece of wood in the ground.

'Post' can also mean 'after'. Like a post-game show is the show after the hockey game. So, it is a word with many uses, not a short form. I hope this helps