Yes, most boards have their own rules about what can be posted on them and how posts should be formatted. A link to these rules can be found on the board page and on the post creation screen.
Since any user can publish a post on any board, the rules serve as a general guideline for all users and determine what and how can be published on the board. Board moderators monitor compliance with these rules and can remove from boards those posts that do not correspond to them.
Also, boards can set restrictions on the types of posts that can be published on them. There are boards that only assume the text format of posts. Other boards, on the other hand, may only allow images or videos to be posted.