1. <character> /enkw/ or /enk/ ENQuire. The mnemonic for ASCII character 5.
2. <chat> An on-line convention for querying someone's availability. After opening a chat connection to someone apparently in heavy hack mode, one might type "SYN SYN ENQ?" (the SYNs representing notional synchronisation bytes), and expect a return of ACK or NAK depending on whether or not the person felt interruptible.