Standards
VT100
One of the dominant computer makers was the Digital Equipment Corporation, Known as DEC. I’m ignoring IBM who had their unique standards (3270). Their earliest terminal in widespread use was the VT52. This was superceded by the VT100 which did all the VT52 did and more. The VT100 inherited a lot of legacy features from the VT52. It still had a keyboard layout you’d not recognise from today’s PCs.
DEC became Digital and they occasionaly brought out new improved terminals: VT220, VT320 … VT520. Eventually DEC sold their terminal manufacturing business to Sun River, who later became “Boundless”. You can still buy VT520 terminals from Boundless. Digital were purchased by Compaq who were then purchased by HP.
ANSI X3.64
The X3 comittee of the American National Standards Institute (ANSI) sponsored the creation of some standards for terminals. In late 1977 these became available.
In August 1978, DEC launched the VT100 terminal, this implemented a subset of the ANSI standard but with some proprietary extensions. Later versions (such as the VT102) extended the set of features.
ISO 6429
The ANSI standards developed into ANSI X3.64–1979. This was later withdrawn and replaced by the International Standards Organisations’ ISO–6429, which was based on the ANSI X3.64 work.
ECMA 48
The European Computer Manufacturers Association (ECMA) published a standard called ECMA–48. Apparently this is pretty much the same thing as ANSI X3.64–1979. It is the only standard of the three available at no charge.
Usability
Apparently all these standards are huge and almost unimplementable. It seems nobody ever implements “ANSI” fully or consistently.