means & full form of w.r.t.
Urwashi has answered your question correctly; I would add few examples only.
Velocity of the boat with respect to ground is 5 Km/hr. It means the velocity of the boat is measured taking ground as the reference. Suppose two buses are running on a road. Bus A has speed 50 Km/hr and bus B has 30 Km/hr. Speed of A w.r.t B is (50 - 30) = 20 Km/hr.
@Urwashi, Very Good! You get a thumbs up for your effort. Your answers are really helpful and appreciated in this forum.
Keep posting guys and have a nice day!