Reading pointless things.
The word originates from a pointless tweet
from T-Shirt Hell on July 28th in which they simultaneously create and define the word.
As is demonstrated in the tweet
that created the word, but not explicitly stated, the word can also be used as a noun in which a "plork" is something pointless that you have read.
Dude check this out - I was just plorking on reddit and found this really cool article!