A plugtest or plugfest is an event based on a certain standard where the designers of electronic equipment or software test the interoperability of their products or designs with those of other manufacturers. It could be literally plugging company A's cable into company B's socket, or a more elaborate test resembling a realistic scenario.
Examples
The technical goal is twofold: check compliance to the standard, and test the effectiveness of the standard. The latter could be the case when the standard is ambiguous. A simplified example is: the width of a plug is prescribed but vendors use different lengths.
Plugtests can be formal and have public test scores or informal and private. Besides helping vendors improve their interoperability, plugtests help create awareness about the standard and can improve transparency on compliancy.