w

The Argument of Perigee (w) is defined as the angle within the satellite orbit plane that is measured from the Ascending Node (W) to the perigee point (p) along the satellite's direction of travel.

The value of the Argument of Perigee can range anywhere from 0 to 360 degrees.

For the ISS TLE:

"308.6263" = 308^o.6263 from the satellite orbit's Ascending Node to its perigee point.