Browsers and standards are in the eternal race. Because there is mismatching in the standards due to different ways of rendering pages, a lot of time of a web designer goes to make up these mismatching (using hacks). As a result, the designer deals with the browsers instead of effective work, losing precious time of work.
A cross-browser is a feature of website that displays and works in all popular browsers identically.
Hack is a correction of a bug or addition of a new feature through the use of other undocumented or incorrectly realized feature. (c) Lurkmore
Dirty hack is a quick solution to any problem in the short term, which negatively affects a code of inner beauty and clashes with its internal structure. (c) Lurkmore