Actually a blog is a kind of website, as they have many similar attributes.
They both occupy a presence on the internet, use an URL or web address, need a host server to keep them online, contain information such as text content, pictures, links and keywords, both benefit from search engine optimisation and can be tracked through Google Analytics.
But why don't we call blogs websites? What is it that makes them different?
The difference is in their programming, and how they make use of Web2.0. The are pre-runners of social networking before Facebook, LinkedIn and Twitter. They thrive on interaction, new content, feeds and optimisation.
Blogs are designed to be self-editable. This means you don't to pay a web designer to make changes or add content. You can update them through very easy access (a username and password) from any computer in the world. The programming is self-contained, and if you can write in Word, you can update a blog.
They thrive on being updated frequently and regularly, their programming is designed to attract search engine spiders who are looking for new content all the time. This is very good for web optimisation which puts blogs higher up the search engines than websites. Another consideration is that blogs are visited by spiders hourly, whereas websites could wait for months.
Unlike websites, blogs only update new material each time it is posted. Every time a website is updated the new stuff supersedes the old content, whereas blogs store previous entries like a news-roll, each post dated accordingly and assigned it's own URL for access at a later date.
Blogs are designed to encourage interactive communication between author and readers. Those who comment can link back to their own sites, and this content is also considered as new material by internet spiders. This concept is not available in ordinary websites, except through sign up forms, and then contributors cannot view afterwards what they have written.
And another consideration to note: blogs are much cheaper to create and maintain!
OK, so what else makes blogs better?
Blogs are created to help businesses to spread their expertise, explain what their business does in different ways, maintain a relationship with their visitors and customers, offer subscription services for regular contact, channel traffic back to relevant websites, and can be fed to other websites like social networking for a higher readership.
Most websites, especially 'brochure style' ones, are static and once created are rarely updated, and can't provide an opportunity to explain everything as space is often limited. In fact, over cluttering your pages with too much information can be counter-productive. Visitors will not return for new content, websites are unlikely to get bookmarked, and only through a sign up form to a newsletter can the business maintain a relationship with potential customers.