The acronym DOH can have a number of meanings including the Department of Health or the Department of Highways. It can also mean Dukes of Hazard. The meaning of the acronym can often be determined by the context.
DOH in Internet slang means Deliriously Overcome with Hilarity. Other definitions include Division of Highways, Days on Hand and Detroit Opera House. It is also the airport code for Doha in Qatar. If it is not intended as an acronym, someone using the word may be making a reference to "The Simpsons," which uses the interjection, "D'oh!", as a sign of exasperation.