A* is optimal if h(n) is an allowable heuristic-that is, providing that h(n) under no circumstances underestimates the cost to reach the goal.

The algorithms of an informed search contain information regarding the goal state. It helps an AI make more efficient and accurate searches. A function obtains this data/info to estimate the closeness of a state to its goal in the system.

For example, Graph Search and Greedy Search.