From LQWiki

Grok is a verb roughly meaning "to understand completely" or more formally "to achieve complete intuitive understanding". It was invented by the science fiction writer Robert Heinlein, and first used in his novel Stranger in a Strange Land, where it is part of the fictional Martian language and introduced to English speakers by a man raised by Martians.

It is now mostly used as slang by science-fiction fans, geeks and some pagans, particularly those belonging to the Church of All Worlds, but is attested more widely.

In the Martian tongue, it literally means "to drink" but is used in a much wider context. A character in the novel (not the primary user) defines it:

"Grok means to understand so thoroughly that the observer becomes a part of the observed-to merge, blend, intermarry, lose identity in group experience. It means almost everything that we mean by religion, philosophy, and science-and it means as little to us (because we are from Earth) as color means to a blind man."

Stranger in a Strange Land Wikiquote

Also

"Grok is a library of Java components for performing various natural language tasks. These include several preprocessing tasks, chart parsing, a large categorial grammar for English (induced from the Penn treebank), and some knowledge representation components (basic coreference, salience tracking, etc.). The library also has a companion kit which provides a GUI interface to the components, several of which are implementations of interfaces in the Quipu OpenNLP API." - freshmeat.net/projects/grok