What is linear search and when is it appropriate to use?

Linear search sequentially checks each element in a collection until finding the target or reaching the end. Time complexity is O(n) worst/average case, O(1) best case. Space is O(1). Use when: data is unsorted, dataset is small, search is one-time, or elements are accessed sequentially (linked lists). For sorted or frequently searched data, binary search or hash tables are preferred.