When you grok something, you just get it — in other words, you totally grasp its meaning. Once you grok your best friend's sense of humor, her jokes won't confuse you but will instead make you laugh hysterically.
The informal verb grok was an invention of the science fiction writer Robert A. Heinlein, whose 1961 novel "Stranger in a Strange Land" placed great importance on the concept of grokking. In the book, to grok is to empathize so deeply with others that you merge or blend with them. The simplest way to think of grok is as truly, deeply understanding someone or something. With any luck, you now grok the word grok.