corank

plural coranks

1. mathematicsThe dimension of the left nullspace of a matrix.
2. mathematicsThe dimension of the cokernel of a linear transformation of a vector space
3. mathematicsThe number of elements of a matroid minus its rank.

   First of all, we can see that coranks are the same for the elements of a conjugacy class.

   1995, William M. Kantor, Lino Di Martino, Groups of Lie Type and their Geometries, page 117