De?nition Instantaneous Description of an FSA:
An instantaneous description (ID) of a FSA A = (Q,Σ, T, q0, F) is a pair (q,w) ∈ Q×Σ* , where q the current state and w is the portion of the input under and to the right of the read head.
w is the portion of the string remaining to be processed. The symbol being currently being read by the FSA is the ?rst symbol of w. If w is empty then the entire input has been scanned and the FSA has halted.