It's from Robert A. Heinlein scifi book "Stranger in a Strange Land".
In the novel native martians do exist and they are very smart. "Grok" it's the martian word for "water" and "to drink". Water is a scarce resource there, and, like here, very important for life.
Drinking is putting water inside you but also occurs that this water becomes part of you.
Then, in that society, drinking is used as the metaphor for understand something in a level that becomes part of you.
I'm a native spanish speaker and I don't know if that word sounds bad in english, but for me the metaphor is so powerful and beautiful that I like it very much.
I have been so conditioned by posting on HN to not reply with the banal, 'this', or, 'good one', that it almost seems wrong to just say, 'thank you for that post'.
Perhaps it's just been by a series of improbable coincidences that in the years I have read forums, IRC logs, books, and articles, I've only seen the term here on HN.
Could be a case of Baader-Meinhof [1], or maybe you haven't been socializing in right forums. The word "grok" has been in popular use on Usenet since the early 1990s at least, probably before, since it's from a 1970s Heinlein novel.
