• A comment is a short remark about an entry on someone else's blog, which will appear underneath their entry. It will not appear on your blog.
• A trackback is a link between two entries on different blogs and allows you to write about someone else's entry in your own blog.

Example: You read on someone else's blog a review of a film currently showing at the cinema. They didn't think much of the film. You could:

Make a comment with a short statement agreeing with them, such as 'Yep, it was rubbish!'

or

Make a trackback putting an entry on your blog going through each point they raised about the film and putting forward why you might disagree.

Related FAQ:

What are trackbacks?