I am coding a tic-tac-toe program that demonstrates reinforcement learning. The program uses minimax trees to decide its moves. Whenever it wins, all the nodes on the tree that were involved in the game have their value increased. Whenever it loses, all the nodes on the tree that were involved in the game have their value decreased, etc. What is the name of the value that each node is decreased by?
I think you mean the leave nodes only which are changed. The other nodes in the tree are calculated during calculating the best move with this tree. The values at the leaves are called utility values in Russel and Norvig's "Artificial intelligence: a modern approach". Some times it is called heuristic value; see https://en.wikipedia.org/wiki/Minimax.