What is a WordPress theme? That’s a simple question… but with a wide range of answers. Let’s start with the definition from the official WordPress Codex:

A WordPress Theme is a collection of files that work together to produce a graphical interface with an underlying unifying design for a weblog. These files are called template files. A Theme modifies the way the site is displayed, without modifying the underlying software. Themes may include customized template files, image files (*.jpg, *.gif), style sheets (*.css), custom Pages, as well as any necessary code files (*.php).

Got all that? Yeah, me neither. Let’s translate. “Collection of files that work together to produce a graphical interface” and “underlying unifying design” – that means the theme is where the design of your site comes from. It determines what the header will look like, where and how the text on each page will be displayed, whether or not you’ll have space for widgets, etc., and – through the use of a cascading style sheet (CSS) – how all those elements will be displayed. “Theme modifies the way the site is displayed, without modifying the underlying software” – It may not be obvious why that’s important… so here’s a quick history lesson. In the early days of the web, every page of a web site was basically just a text file with special code to handle the formatting. This created two problems:

  1. Every time you created a page, you had to replicate all that formatting code.
  2. If you wanted to change the formatting, it had to be changed on every page.

A content management system – CMS, in geek-speak – solves that problem by separating the content of your site from the presentation instructions. A CMS stores all your site content – words, pictures, etc., in a database and stores the site layout instructions in the theme, and then puts them together to make Web pages. WordPress takes that one step further by making it very easy to switch between themes. You could build your entire site in the Twenty Twelve theme (the WordPress default) and then switch to something else in a matter of minutes. “Themes may include customized template files” – Almost every WordPress theme includes a few basic files… the templates for the site header and footer, a blog post template, a page template, maybe a category page. Fairly simple. But the theme system is endlessly customizable. There are highly specialized themes that allow you to use WordPress as a portfolio, or a classified advertising marketplace, or just about anything else you can imagine.

Theme vs. Design

Much of the look and feel of your site is defined by the theme, but “Theme” and “Design” are not always synonymous. Some themes don’t allow for much design flexibility. But some will allow you to change colors and fonts, the layout of your pages, the position of sidebars, etc. Generally speaking, it is much easier to customize the look of a theme than the functionality, so bear that in mind when you’re selecting yours.