Single concave is basically described as a single curve from rail to rail. The deepest part of the curve is along the stringer or centre of the surfboard. The depth of a single concave can vary but it is usually deeper than a double concave.
On Single Concave surfboards, only one concave directs water from the front of the surfboard to the fins and tail of the board. The design allows for faster surfing and works very well in big, clean waves.