The transport layer is a crucial part of the OSI model, responsible for ensuring reliable data transfer between devices over a network. It manages the segmentation of data into smaller packets, which can be sent efficiently and reassembled at the destination. This layer also handles error detection and correction, ensuring that any lost or corrupted packets are retransmitted. Two main protocols operate at the transport layer: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP provides a connection-oriented service, guaranteeing delivery and order of packets, while UDP offers a connectionless service, prioritizing speed over reliability.