in formula F=DP/DT, d stands for what?
This is a standard equation which describes the Newton's second Law of Motion; it relates Force with momentum.
F = dp/dt means that the force applied on a body is directly proportional to the change in its momentum. Here momentum refers to as the amount of motion contained in a body. So, in other words, the equation represents the fact that force causes a change in the motion (or state) of a body. This is a fundamental definition of force as far as classical Newtonian mechanics is concerned.
The above relation can also be expressed as
F = dp/dt = d(mv)/dt
F = ma
force is also directly proportional to the acceleration (or retardation) produced in a body.