Firth is a word in the English and Scots languages used to denote various coastal waters in the United Kingdom, predominantly within Scotland. In the Northern Isles, it more often refers to a smaller inlet. It is linguistically cognate to fjord, which has a more constrained sense in English. Bodies of water named "firths" tend to be more common on the Scottish east coast, or in the southwest of the country, although the Firth of Clyde is an exception to this. The Highland coast contains numerous estuaries, straits, and inlets of a similar kind, but not called "firth" ; instead, these are often called sea lochs. Before about 1850, the spelling "Frith" was more common.

Rough Firth is an inlet on the northern coast of the Solway Firth in the Stewartry area of Dumfries and Galloway, Scotland. The firth lies between Almorness Point and Castlehill Point, and contains Rough Island. The village of Kippford stands near the head of the firth where the Urr Water reaches the sea; the only other coastal settlement of any size is Rockcliffe. The area is designated as the East Stewartry Coast National Scenic Area, one of the forty national scenic areas (NSAs) in Scotland.