What's the difference between a forum and a post bar?

The difference between forum and post bar is as follows:

Forum: It is an electronic information service system on the Internet. You can post information or make comments. Strong interactivity and rich content. The forum is divided into several sections according to different themes. Users can read other people's opinions on a topic, or they can post their own ideas to the forum without reservation. Generally speaking, forums also provide mail functions. If you need to communicate privately, you can also send what you want to say directly to someone else's mailbox.

Post Bar: It is equivalent to an open forum, such as Baidu Post Bar, which has a high degree of freedom and can post without registration. And it's easy to apply for bar owners, be a moderator and set up your own forum. Now there are all kinds of topic posts, many of which can only be found by keywords, but not by lists.