QUIC is a transport protocol designed to provide secure, multiplexed application transport over UDP while implementing reliability and congestion control in user space.

A QUIC connection contains multiple independent streams. Loss affecting one stream need not prevent already available data from other streams from being delivered, avoiding connection-wide transport head-of-line blocking between streams.

QUIC integrates cryptographic handshaking with transport setup rather than layering a separate TLS record transport over TCP. It also identifies connections independently of a fixed IP-address/port pair, allowing a connection to survive some endpoint-address changes such as moving from Wi-Fi to mobile data.

QUIC still runs over IP and must share congestible paths responsibly. Its significance is architectural: transport features that TCP couples into one ordered byte stream can be reorganized around encrypted, multiplexed streams and explicit connection identity.