SOCK_STREAM A sequenced and reliable bidirectional connection-based stream. Most common in use.
SOCK_DGRAM An unreliable, connectionless socket that transmits data of a fixed length. Very good for streaming of data where reliability is not a concern.
SOCK_SEQPACKET Similar to stream sockets, except data is transmitted and received in fixed-length packets.
SOCK_RAW A raw socket connection, useful for performing ICMP (Internet Control Message Protocol) operations such as traces, pings, and so on.
SOCK_RDM A reliable but unsequenced socket similar to that of SOCK_DGRAM.