the space factor when determining the efficiency of algorithm is measured by

The space factor when determining the efficiency of an algorithm is measured by counting the maximum memory required by the algorithm during its execution.

In standard data-structures/algorithms terminology, this is usually referred to as the algorithm’s space complexity, i.e., the amount of extra memory (besides input and output) that the algorithm needs at any point in time, typically expressed as a function of input size using Big O notation (like O(1)O(1)O(1), O(n)O(n)O(n), etc.).