ASP (Active Server Pages) is a script engine. It is used for creating pages that update every time a user visits (dynamically generated). An example of this would be a news website, where each time a user visits the website, it is up to date with the latest news.
PHP is a scripting language that can be embedded into html, originally used to produce dynamic web pages and makes them more interactive. An example of a website that uses PHP is wikipedia, where users are allowed to edit pages. It also offers the function of password protecting web pages. It is a free software.
ColdFusion is an Adobe program focusing on application development. It has its own language which is also often simply called ColdFusion, even though its official name is ColdFusion Markup Language (or CFML). Its original purpose was to connect databases and HTML webpages, although it has since taken on a life of its own. It often works with Java and .NET frameworks. CFML is a cross between ASP/PHP and HTML, sharing similarities with all of them.
Cascading Style Sheets (CSS) are a way to alter the visual layout/design of HTML webpages. Even if the CSS isn't working, the web page will still work, which is a major advantage.
The above is part of an example css taken from an internet forum that I have edited in the past.