Definition - What does Open Transport mean?
Open Transport is a communications protocol for networks and Macintosh operating systems.
In 1995, Open Transport replaced MacTCP, which was Mac’s TCP/IP standard implementation through OS version 7.5.1.
Techopedia explains Open Transport
Open Transport supports AppleTalk and launched with the Peripheral Component Interconnect (PCI)-based Power Mac 9500 (version 7.5.2). Open Transport is built on Mentat Portable Streams (MPS), which is a Unix-originated System V STREAMS platform that supports Transmission Control Protocol/Internet Protocol (TCP/IP).
Open Transport was eventually replaced by Mac OS X, but Open Transport application programming interfaces (API) are available as compatibility layers for older applications.