A discrete graphics card is one that can be replaced or upgraded with another discrete graphics card.
Integrated Graphics/iGPU is a graphics processing unit that is integrated into the CPU or in the motherboard chipset on some older generation motherboards and is not replaceable or upgradable without replacing the device that it is integrated into.
In most laptops the Graphics Processing Unit is integrated or the GPU chip is soldered to the laptop's motherboard and is not upgradable or replaceable.
There are some expensive gaming laptops that have upgradable mobile graphics cards. Some even have two mobile graphics cards in SLI or CrossFire.
In the past, integrated graphics meant a chip soldered into the motherboard of a laptop like the Radeon HD 4250 and the Intel GMA 3100; basically integrated into the north bridge. Currently integrated graphics means the graphics core inside the CPU (or APU as AMD prefers to call them).
A discrete graphics card is a graphics card that for the vast majority of laptops are soldered into the motherboard like the Radeon HD 7730m and nVidia GT 640m.