Linked lists are data structures where each node points to the next node or end of the list. There are different types of linked lists including singly linked lists where each node has a data field and next pointer, and doubly linked lists where each node has next and previous pointers. Linked lists are used to implement common data structures like stacks, queues, and databases. The document discusses using linked lists to parse and store a 10GB Harvard library metadata dataset in MARC21 format into a MongoDB database to create a searchable web interface.