Browser - By definition a "Web Browser is computer software that interprets the markup of files in HTML, formats them into Web pages, and displays them to the user". In better terms, it is a computer program that people use to access the internet. The most well known web browsers are programs such as AOL, Netscape, Internet Explorer, and Safari.
Cross-Browser Issues - If you look at a web page on your computer, and then look at the same web page on a different computer, chances are the page looks "different"....colors may look different, font shapes and sizes may differ, and the position of pictures and things on the page may be in a different place. This "difference" is commonly called "cross-browser issues". Each browser, and each version of each browser, tends to interpret and display HTML in different ways. We have not yet found the guy we can blame for this....when found, you'll hear about it as he will be the guy being attacked by a mass of computer nerds! Nevertheless, cross browser issues are things that must kept in mind when developing a web site.