Key-value pairs are a fundamental data structure used in programming and databases. They consist of two linked elements: a key, which is a unique identifier, and a value, which is the data associated with that key. This structure allows for efficient data retrieval, as you can quickly access the value by referencing its key. In many programming languages, key-value pairs are implemented in data types like dictionaries in Python or hash maps in Java. They are commonly used in NoSQL databases to store and manage data, enabling flexible and scalable data organization.