朴 or pu often gets translated in Daoist texts as "uncarved block." It refers to a primal state of simplicity, but not dullness, prior to the arising of distinctions and thinking. Daoists, and the Buddhists who encountered them, used it as a metaphor for Mind. It captures in short form, for example, what "Affirming Faith in Mind" hammers home in long form.
But there's a danger in just thinking, "Oh, ok, 朴, I get it," thereby adding another idea to one's collection. This is why koan training is such an important part of practice. 朴 is what Ummon kept throwing at the pious and fawning when he put Zen practice and the profundity of Buddhism on the level of taking a dump and wiping your ass. How many of the koans are meant to keep our feet firmly on the ground? It's the shit stick, dummy. It's the hempen shirt, for goodness' sake. It's the price of rice or gas or cars, goofball. It's the water in the pot, the storehouse, the interstate, the gate, the blinds, the Wal-Mart, the Nordstrom, the flower, the high end restaurant, the derelict neighborhood, the oak and the weed, you idiot.
Separate for a second zazen from washing the dishes, working the garden, taking out the trash, going to work, making love, diapering the baby, dealing with the teenager, and all the endless kaplas would not suffice for you to make your way back to reuniting them.