Technical
Argument of Perigee
The orbital element giving the angle, within the orbital plane, from the ascending node to the point of closest approach (perigee).
The argument of perigee orients the ellipse within its orbital plane by specifying the angle from the ascending node to perigee. It determines where in the orbit the spacecraft is closest to Earth.
For eccentric orbits it is operationally important — for example, Molniya orbits place the argument of perigee so that apogee dwells over the desired high-latitude region.