What's the difference between a programming language, a scripting language, and a markup language?

The primary difference between a "programming language" (C, C++, VB etc.) and a "scripting language" (PHP, ASP, JSP, JavaScript, VBScript)is that code written in a programming language needs to be compiled before it is run. Once it is compiled, it can be run any number of times.

Scripting languages, on the other hand, are interpreted at run-time. This means that every time you want to run the program, a separate program needs to read the code, interpret it, and then follow the instructions in the code. Compiled code has already been interpreted into machine language, so it is will typically execute faster because the conversion into machine language has already been done.

Markup languages (HTML, XML) are somewhat different from both of the others. A markup language is simply a set of tags that are used to "mark up" text documents so that sections of text can be logically arranged and labeled. These documents can be viewed as plain text, or, more commonly, are viewed through a browser. The browser parses the document, looking for markup tags, and it then arranges the text and/or formats it according to the values in the tags.