A singly linked list is a data structure that consists of a sequence of elements, called nodes. Each node contains two parts: the data it holds and a reference (or pointer) to the next node in the sequence. This structure allows for efficient insertion and deletion of elements, as nodes can be easily added or removed without reorganizing the entire list. In a singly linked list, the first node is known as the head, while the last node points to null, indicating the end of the list. This linear arrangement makes it easy to traverse the list from the head to the tail, but accessing elements by index is less efficient compared to other data structures like arrays.