Visual Studio Express is a generic name for various free (as in beer) versions of VisualStudio released by Microsoft aimed at hobbyists. 
Each version only supports one language or technology (e.g., Visual Studio Express for C# vs. Visual Studio Express for Visual Basic vs. Visual Web Developer Express) - although you can install of the free versions side by side with no difficulties (hard drive space not withstanding), and Microsoft provides a DVD image containing all of them. 

The Express versions have far less features and functionality than Visual Studio - most notably they cannot install Visual Studio extensions (without incurring the wrath of Microsoft's IP team anyway), thus making the IDE useless for languages like IronPython or F# (FsharpLanguage).