The significand[1] (also coefficient,[1] sometimes argument,[2] or more ambiguously mantissa,[3] fraction,[4][5][nb 1] or characteristic[6][3]) is the first (left) part of a number in scientific notation or related concepts in floating-point representation, consisting of its significant digits.
[7][8] Although the other names mentioned are common, significand is the word used by IEEE 754, an important technical standard for floating-point arithmetic.
The term significand was introduced by George Forsythe and Cleve Moler in 1967[16][17][18][5] and is the word used in the IEEE standard[19] as the coefficient in front of a scientific notation number discussed above.
To understand both terms, notice that in binary, 1 + mantissa ≈ significand, and the correspondence is exact when storing a power of two.
The implicit leading 1 is nothing but the hidden bit in IEEE 754 floating point, and the bitfield storing the remainder is thus the mantissa.