What is the difference between TCP and UDP in networking?

TCP and UDP both deliver data but with very different priorities. TCP is connection-oriented and reliable: it sets up a connection first, numbers the packets, checks they all arrive, re-sends lost ones, and keeps them in order. This makes it slower but trustworthy, so it is used for web pages, email and file transfer where every byte must arrive correctly. UDP is connectionless and unreliable: it just fires packets off without setting up a connection or checking delivery, so it is faster with less overhead. UDP suits live video, online games and voice calls, where speed matters more than a few lost packets. For exams, summarise it as TCP equals reliable but slower, UDP equals fast but no guarantee of delivery or order.