What is the meaning of term called "Back pressure" in Hydraulic system?

Back pressure occurs when hydraulic flow in the return line is restricted and causes a buildup of pressure backward through the line. This is undesirable as it robs the entire system of potential flow as the pump now has to produce more power to overcome the back pressure.

pressure builld up back through the hydrualic line back into the working fluid reserviour.

Back pressure in hydraulic system is the pressure when the flow of return in line is restricted it can cause damage to hose pipe

back pressure in a hydraulic system can occur when the hydraulic flow in the return line is restricted 

when there is hydraulic flow in a line and the flow  have a sudden shut off the flow there will be a pressure back in the line which could destroy the line that is call back pressure

pressure opposed to the desired hydraulic flow

 In my understanding the pressure before the pump is called back pressure as the the pressure after the pump is called system pressure, therefore in a close circuit of any hydraulic system the back pressure in fact restrict to system pressure and hens causes extra load on system pump to work more and overcome the undesirable resistance to flow of hydraulic fluid.

Back pressure is defined as the overcoming of hydraulic pressure by any exhaustion pressure.

Back pressure in closed conduits (pipeline flows) can be developed or caused by any blockage in the path of flow streamlines or reduction in flow area due to sudden change in cross sectional area of conduit.

It can happen both in gravity as well as pressurized pipes. In case of more flows than the pipe capacity, hydraulic grade line raises with the increase in flow. In pressure pipes, it can cause water surge due to sudden closure of valves or pumps.

the pressure encounterered on the return side of the system

An obstruction may be treated as the resistance to flow which may ulter the hyraulic characteristics of the the flow and may be treated as slow process. whereas truely speaking,  back pressures are surge due to sudden upward pressure change , water hammer due to sudden reversal of flows and may be treated as rapid process.