Linear search
Also known as: Sequential search, Brute-force search
Linear search scans elements one by one until it finds the target or exhausts the collection. Works on unsorted arrays and linked lists; no preprocessing beyond what you already have.
Time $O(n)$ worst and average for a successful search in a random location; $O(1)$ best when the target is first. No extra memory.
Use when $n$ is small, data is unsorted and searched once, or you cannot reorder or index the structure. For many lookups on a static list, sort once and switch to binary search, or put keys in a hash table.