[from the novel 'Stranger in a Strange Land', by Robert A. Heinlein, where it is a Martian word meaning literally 'to drink' and metaphorically 'to be one with']
vt. 1. To understand, usually in a global sense. Connotes intimate and exhaustive knowledge. Contrast zen, similar supernal understanding as a single brief flash.
See also glark.
2. Used of programs, may connote merely sufficient understanding.
"Almost all C compilers grok the 'void' type these days."