Double Lugging

Does double lugging only pertain to circuit breakers or can it pertain to the load side of a meter socket?

Does the NEC mention anything about double lugging?

Thanks for any information provided.

It could pertain to anything. Or in other words, anyone could do things anywhere which they should not do or would be ok to do.

The question is... Did the manufacturer design the lugs for only one wire or for two wires? Or does the manufacturer's specifications say that two wires are permitted on that lug/screw terminal?

Here is an example of a manufacturer's specs for lugs.
http://www.state-electric.com/files/catalogs/siemens_industrial_controls/17_067-069.pdf

P.S. Also what wire is connected in the case of a neutral bar. The manufacturer may say it is ok to connect two ground wires, but not ok to connect two neutral wires - same size wires, same screws, same bar - different use.