The value of a play means some sort estimate of the number of points gained (or lost) by it. There are two main approaches:
The value of a threat is the value of a follow-up move if the threat is ignored.
PJTraill: I have not found a page with this sense of value, to which Bill Spightís never completed Counting without Tears refers, so I have made this as a place-holder. It is of course close to counting, but that does not actually talk of the value of a move. Either that or this could be extended.