Well, double disc and ABS are two relatively different terms and we will know the difference by considering Pulsar 180 as an example. A disc brake is a better braking system when compared with the old drum braking system on the bikes. The older generation of Pulsar 180 came with a single disc while the current generation carries double disc as standard on the bike.
Double disc means that the bike has two disc brakes around its both wheels. It can be one disc at the front and one at the rear or even could be two disc brakes at the front and drum brake at the rear. It has no relation to ABS as such. Pulsar 180 was first fitted with a front disc brake while it now comes with a rear disc brake as well. Both the brakes are operated through different levers.
ABS, on the other hand, is a technology that works side by side with the brakes of an automobile. It is actually a sensor along with a computing device which counts the rotation and speed of a wheel. This helps it decide within few milliseconds that how much braking power is to be transferred to the wheel in case sudden brake is applied. The working of the system is actually simple.
It holds and releases the caliper automatically in order to avoid wheel locking and brake effectively. Double disc brakes can help you to stop the bike in lesser time than a single disc brake but when it comes to braking on sand, water or other unfavorable condition, the double disc brake setup will even let the bike slip away in seconds. A motorcycle with ABS and double disc will actually not skid away and brake effectively.