What's an industry standard in electrical engineering?
Tautologically, something is industry standard if it's standardised by the industry. That means there will be a standards body issuing documents which define what the standard is.

For example, DIN standardise e.g. DIN plugs such as on PS/2 keyboards and audio equipment. JEDEC various things to do with ICs. IEEE. ISO. British Standards Institute for our BS1363 plugs. MILSPEC for high durability. There are quite a lot of these but they're not very search-friendly.

(The PS/2 keyboard is a good example of a defacto standard that didn't come from a body, rather from everyone making IBM compatible equipment. Defacto standards are harder to pin down.)