In medieval music, ambitus is a Latin term literally meaning enclos[ur]e, and in Medieval Latin means the "range" of a melodic line, most usually referring to the range of scale degrees attributed to a given mode, particularly in Gregorian chant. In Gregorian chant specifically, the ambitus is the range, or the distance between the highest and lowest note. Different chants vary widely in their ambitus. Even relatively florid chants like Alleluias may have a narrow ambitus. Earlier writers termed the modal ambitus "perfect" when it was a ninth or tenth, but from the late fifteenth century onward "perfect ambitus" usually meant one octave, and the ambitus was called "imperfect" when it was less, and "pluperfect" when it was more than an octave.