A. "Recursion" comes from mathematical recursion and mathematical induction.
B "Recursion" is the same as recursive formula, starting from the basic calculation of recursion, from the previous term (n- 1 term) to the last term (n term) until the final result is obtained.
C. "Recursion" refers to substituting the last item (i.e. the nth item) into the previous item (the n- 1 item) until the result is obtained based on recursion, and then obtaining the result from the last item calculated by the previous item until the final result is obtained.
D "Recursion" is the method to calculate the nth term from the first n- 1.
Correct answer: ACD