Question

What do you mean by work against gravity?

Answer 1

working against gravity is doing something unusual and almost next to impossible or may things which are very hard to do or in simple against the laws and basic manners or usual routine

Answer 2

Work done by a body is against the applied force if the displacement is in a direction opposite to the force. In the case of gravity, if a body is lifted above the ground, work is done against gravity.  All bodies with mass are attracted towards the earth by gravity, so when a body is lifted one has to do work to raise it.  Work done against gravity = Force x Displacement = Weight x Height = mgh = gravitational potential energy stored in the body.