Interstat code

From Memory Alpha, the free Star Trek reference.

Interstat code was a type of inter-stellar communications code used primarily during the 21st century. By the second half of the century the code was outdated and rarely used.

The inhabitants of Terra 10 colonized that planet during the era of interstat code and still relied on it for communication nearly 100 years later. (TAS: "The Terratin Incident")