A browser is a program that downloads HTML documents, images, and other content and renders it all nicely for the user to look at. And feel free to come up with a better definition.

Examples include Mozilla (see MozillaNotes), InternetExplorer, Konqueror, Opera, Firebird?, Lynx... the list is endless.

Opera has the least broken implementation of CSS (which doesn't necessarily say much) and Konqueror has the most broken one. InternetExplorer just tends to be... idiosyncratic in its interpretation of the standard. (Sigh.)

The first graphical WebBrowser (from c. 1992?) was NCSA Mosaic.

Under X on Linux I recommend Mozilla, on a Linux console I recommend lynx(1) or links(1), depending on your tastes (and resolution).