TCP
In plain terms
A core internet protocol that delivers data reliably and in order.
Going deeper
Transmission Control Protocol establishes a connection, splits data into packets, confirms delivery, and reassembles them in order, retransmitting losses. It trades a little speed for reliability.
Under the hood
Provides ordered, reliable, congestion-controlled delivery via a three-way handshake and acknowledgments; the cost is latency versus UDP's fire-and-forget.
Examples
HTTP, SSH, email (SMTP), file transfers, database connections.
Think of it like...
Like registered mail with tracking: every package is numbered, confirmed on arrival, and resent if lost, so the full message arrives intact and in sequence.