What is the difference between a blog and a forum?

With a blog, you set up your account and site, design it to look the way you want it to look, add advertising in some cases, and write regularly. Over time, both by your own design and as a result of what you've written, your blog develops a "personality". You can elect to allow comments or not. Blogs are often devoted to a specific topic, although some are devoted to a number of topics (for example, "All the things I've thought" or "What I did today") that, essentially, are only related by virtue of the fact that the same person wrote them.

A forum belongs to someone else (a company, an online site, a non-profit organization, or anyone who who creates and runs the forum). A forum is a collection of posts offered by the general public, often in a question-and-answer format although some forums are nothing but comments on a post that, itself, was nothing but a comment.

Some forums require contributors to register, which allows them to set preferences with regard to who can contact them, how their posts appear, or whether they receive e.mails when posts are made. Some forums offer separate blogs to go with membership.

There are forums which, for the most, cover topics that are very specific. (I once ran into a Scion forum, which was about nothing but that particular automobile.) Forums are often primarily devoted to one topic (it could be a television show, a disease, a phone model, anything) but will also offer a section for anyone wishing to post on "off-topic" matters.

While a blog may be a collection of one person's writing on something like being the mother of child with autism or else a presidential election, a forum is more a collection of the public's shorter comments on a topic. In a forum for parents of autistic children, for example, a number of people may contribute their questions, thoughts, experiences, or links they believe will be helpful.

Most blogs are created on sites aimed specifically at offering blogging accounts to members, although an individual could obtain his own, individual, website and use it for the purpose of blogging.

By the same token, if one parent starts a blog about having an autistic child (or, say, autism in general), that person will write more extensively, may offer helpful links, may invite the comments of others, etc.; but the focus of the blog will remain on main, contributing, writer.

Forums may place ads on pages, and some even allow for revenue sharing by each contributor. The creator of a blog can arrange to have ads placed on the blog, and those ads can result in earnings for the blog creator.

From the perspective of the person who finds a blog and contributes comments or helpful information, there can, in ways, be little difference between offering helpful information on a forum versus a blog; however, who reads those comments will depend on how popular, well known, and searchable a blog or forum is. Posting a comment on "Fred's Blog About His 2000 Ford Taurus", which you happen to accidentally run into, but which may not get many views, is means your visitor's comment is less likely to be seen than if you posted the same comment on a large, well known, Ford site or forum with a high search engine page rank.

On the other hand, if "Fred" ever finds a way to make his blog more well known and more highly ranking in the search engines, the comment you post on his blog will, of course, be seen by more people.