It's what you're probably using to read this right now. A browser, or web browser (same thing), is the program people use as their interface to the World Wide Web. It interprets HTML code including text, images, hypertext links, java applets, etc. allowing you to view web sites and navigate from one to another.
Phoenix (hah, really old, this was Firefox before it was Firebird even ;)
http://www.mozilla.org/projects/phoenix/
http://www.mozilla.org/projects/firefox/
Netscape http://www.netscape.com/computing/download/
Opera http://www.opera.com/download/
Lynx http://gd.tuwien.ac.at/infosys/browsers/lynx/
Lynx for DOS/Windows http://www.fdisk.com/doslynx/lynxport.htm
w3m http://prdownloads.sourceforge.net/w3m/
Apple Safari http://www.apple.com/safari/download/
Mosaic http://archive.ncsa.uiuc.edu/SDG/Software/mosaic-w/releaseinfo/download.html
Konqueror http://www.konqueror.org/
Wikipedia:List_of_web_browsers
Amaya http://www.w3.org/Amaya/
SlipKnot http://www.micromind.com/slipknot.htm
SeaMonkey http://www.mozilla.org/projects/seamonkey/
3B (3D-browser) http://www.3b.net/browser/how3bworks.html
Salamander http://members.tripod.com/OskarK/salamander.html
Avant http://avantbrowser.com/
Arachne http://home.arachne.cz/
X-Smiles http://www.xsmiles.org/index.html
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