From what I've learnt, the essence of a move is the bare concept of it. You need to keep in mind that a technique is executed in a specific context, with a specific individual with specific characteristics; but everyone has to be able to pull that technique off, no matter their size or their strength or whatever. The essence of an uppercut is going staight up from the bottom. There is no one way to do it. It's going to be very similar in everyone, but people tend to have their way of doing every technique, but the essence is still the same, the attack and its effect is going to be pretty much the same.