Ask anyone who makes or watches ASMR and you'll likely get a slightly different answer from each person. Here's mine.

Bob Ross is widely regarded as the unintentional grandfather of ASMR. His painting videos were not only mesmerizing and beautiful, but they were also relaxing due to his soft voice and calm demeanour. Everything seems to slow down when watching Bob Ross perform his art and although it may not have been intentional at the time, even the sound of the brush on the canvas would be enough to trigger the ASMR response in many people, myself included. 

ASMR is a relaxing feeling, that's it. But aside from feeling relaxed, ASMR has a very specific sensation we call 'tingles'. 

Starting in the head and often working its way down the body, the 'tingles' are a sensation that is triggered by various visual and auditory stimuli. It might be Bob Ross's voice, it might be someone whispering very closely into your ear. It could also be someone tapping very gently on a keyboard or perhaps someone intricately describing something to you. Something often mundane and otherwise boring (such as folding towels) could be a trigger for one person, but not another. 

Essentially, ASMR is relaxation with a tingling sensation that tends to serve one main purpose. Sleep. 

Millions of people fall asleep every single night to the sounds or visuals of their go-to ASMR videos. 

That is ASMR.