# Equation for $N$-body problem using Jacobi Coordinate

For reference on Jacobi Coordinate used for solving 2-Body problem, I referred Wikipedia Jacobi Coordinate, and on looking at those equation I can't get the meaning of the symbol q in the equation for Vector to center of mass,

Rjk = ( mjqj + mkqk )( mj + mk )

It would be helpful if some one could help.