IANA-reserved, and the boundary: the lowest port an unprivileged process can bind.
RFC 6335 puts 1024–49151 in the User (registered) range, and IANA holds 1024 itself Reserved, so nothing standard is assigned to it. Its real significance is structural — it is the first port a non-root process may bind on a Unix-like system, and older Windows releases (2000, XP, Server 2003) started their dynamic client-port allocation at the low end of 1025–5000, with Vista and Server 2008 moving to 49152–65535. nmap labels 1024 kdm, after KDE's display manager, which is a historical guess rather than a live protocol.
Expose with care
Anything listening here is unprivileged and locally chosen. That is not automatically dangerous, but it is unidentified until you look, and firewall rules written around the 1024 boundary are about privilege, not trust.
$ sudo lsof -nP -iTCP:1024 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.