Answer: Frequency analysis
Explanation: When talking about frequency analysis, it basically refers to taking cognizance of how prominent something exist in terms of the number of times it occurs, distinguishing events in terms of their number of occurrence. The frequency analysis technique is used to study, but xamine or evaluate the how often a letter occurs in a ciphertext, it simply means counting the number of occuences of the alphabets of a ciphertext. This method is used to crack classical ciphers by taking advantage of the fact that some letters of the alphabet occurs more often than others.