TCP is a core communication protocol that ensures reliable delivery of data over networks. It breaks messages into packets, numbers them, and reassembles them in the correct order on arrival. TCP also manages error detection, retransmission, and flow control, which guarantees data integrity. While reliable, TCP introduces some latency and requires more resources compared to lightweight protocols like UDP. In IoT, TCP is often used when accuracy is more important than speed, such as in firmware updates or secure transactions. Its reliability makes it essential for critical IoT operations.