They used to be micro-sites but today they are usually part of a regular website or a web site is created with blogging software, like my favorite, WordPress. A nickname for a WordPress web site is a "blog site".
You can keep blogs updated, ideally twice a week, with informative content that demonstrates your expertise. You also have the ability to post your thoughts in response to a blog post that someone else made or a current event.
This makes blogging social, current and very important to your overall internet marketing strategy.
Blogging is the foundation to all your other online marketing efforts because regular blogging humanizes you, it's very inexpensive and creates a feeling of trust between you and your potential customers.
The trick for proper blogging is not to make your blogs a hard sell, but to educate your readers and demonstrate your expertise. Each post should speak to your target market. If your audience feels engaged they will purchase your products or services, when they are ready.