Concurrent data structures are specialized data structures designed to allow multiple threads or processes to access and modify them simultaneously without causing inconsistencies or errors. They are essential in multi-threaded programming, where different parts of a program may need to read or write data at the same time. Examples include concurrent queues, stacks, and hash tables, which use various techniques to manage access and ensure data integrity. These structures often implement synchronization mechanisms, such as locks or atomic operations, to control access. By efficiently managing concurrent operations, they help improve performance and responsiveness in applications, particularly in environments like multicore processors and distributed systems.