A dovetail cutter is an endmill whose form leaves behind a dovetail slot, such as often forms the ways of a machine tool.
As the number of cutting edges increases, your feed rate should increase to prevent burning and premature tool dulling. More flutes reduce chip load and improves surface finish if feed rate remains the same. The most common flute numbers for general milling operations are two (better space for chip ejection) and four (better surface finish).