WYSIWYG is an acronym for "what you see is what you get". It refers to a very neat and visually pleasing type of user interface, one in which what you see on your computer screen is what you will see printed on paper. Text editing programs were among the first to use WYSIWYG, but it is now used widely in word processing, graphics programs, and desktop publishing as well. WYSIWYG is pronounced "whizzy-wig".
Programmers will tell you that authentic WYSIWYG is pretty rare, and that the idea is more accurately expressed as WYSIAWYG (what you see is almost what you get) or WYSIMOLWYG (what you see is more or less what you get).