Similar to SCTP, SSH and HTTP/2, QUIC features separate logical streams within the physical connections. A number of parallel streams that can transfer data simultaneously over a single connection without affecting the other streams.
A connection is a negotiated setup between two end-points similar to how a TCP connection works. A QUIC connection is made to a UDP port and IP address, but once established the connection is associated by its "connection ID".
Over an established connection, either side can create streams and send data to the other end. Streams are delivered in-order and they are reliable, but different streams may be delivered out-of-order.
QUIC offers flow control on both connection and streams.