Wiktionary
n. A flat expanse of mud at the edge of a body of water, regularly inundated by e.g. tide action.
WordNet
n. a tract of low muddy land near an estuary; covered at high tide and exposed at low tide
Usage examples of "mud flat".
He walked away from them, quickly, his small body silhouetted against the sun, across the weed-ridden mud flat.
If the grass islands had not suddenly given way to a mud flat, they would not have seen the other bank until they trod on it, but as it was, they got a clear glimpse of the last stretch of swamp before they had to cross it.
He struggled across the mud flat, the ooze and rotting slime sucking at his boots.
After he's proceeded a mile or so, the track crosses a small, open mud flat where he gets a good look at the footprints, all made by bare feet with enormous, bizarrely splayed toes.
Confounded, Giles took a hesitant step onto the cracked, dry mud flat.
The trucks rattled through town and lined up on the vast mud flat outside the sawmill.
But they did not fly across the whole of it, for the mud flat was quite large.
Proceeding along the verge of the swamp they came out on a knoll overlooking a hundred yards of mud flat, with the sluggish First Sea beyond.