Configuration or Instantaneous Description (ID) :
A configuration or an instantaneous description (ID) of PDA at any moment during its computation is an element of 
describing the current state, the portion of the input remaining to be read (i.e. under and to the right of the read head), and the current stack contents. Only these three elements can affect the computation from that point on and, hence, are parts of the ID.
The start or inital configuartion (or ID) on input 
is 
. That is, the PDA always starts in its start state, 
with its read head pointing to the leftmost input symbol and the stack containing only the start/initial stack symbol, 
.
The "next move relation" one figure describes how the PDA can move from one configuration to another in one step.