An Etymological Dictionary of Astronomy and Astrophysics

The factor multiplying the variable in a term of a → binomial expansion. For example, in (x + y)⁴ = x⁴ + 4x³y + 6x²y² + 4xy³ + y⁴ the binomial coefficients are 1, 4, 6, 4, and 1. In general, the r-th binomial coefficient in the expression
(x + y)ⁿ is: (n,r) = n!/[r!(n - r)!].

See also: → binomial; → coefficient.