A blog’s an informative piece of content published online, which may or may not have a comments section.
A discussion forum allows people to ask and answer questions, learn, and get peer-to-peer support, but lacks additional features to facilitate engagement.
An online community is a group of people with shared interests. It may include blogs and forums, plus other sections like job postings or resource libraries. Online communities take longer to set up but offer an all-in-one solution to add value and keep their members engaged.