This is a potential security issue, you are being redirected to https://csrc.nist.gov.
Refers to the rank of a matrix in linear algebra over GF(2). Having reduced a matrix into row-echelon form via elementary row operations, the number of nonzero rows, if any, are counted in order to determine the number of linearly independent rows or columns in the matrix.
NIST SP 800-22 Rev. 1a