Flat
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
A place covered with water too shallow for navigation with vessels ordinarily usedfor commercial purposes. The space between high and low water mark along the edge of an arm of the sea, bay, tidal river, etc.
Thomas v. Hatch, 23 Fed. Cas. 946; Church v. Meeker, 34 Conn. 424; Jones v. Janney, 8 Watts & S. (Pa.) 443, 42 Am. Dec. 309.