Custom Fields

Custom Fields are WordPress' way of giving you the possibility to include some additional information in your blog posts (information that you don't want to display directly on the frontend). In essence, Custom Fields are a kind of semi-programming tool--they are not exactly code as understood by PHP programmers, yet they do give you the possibility to tweak your content in a certain, non-stock way. Many WordPress themes use various Custom Fields to style the individual aspects of posts. For example, some theme creators use Custom Fields to disable the sidebar on certain posts or include various typographic elements.

As another example, let's say you are a gadget reviewer and every blog post is a review of some cool new thing. Every time you write a review, you're writing it about a product that's made by some company, and you'd like to have that company's logo associated with the blog post. You can make a custom field called company_logo and the value can be the path to the logo image:

To display or make use of this Custom Field information, you either have to modify your theme files manually or use a plugin.