One of the 10 key characteristics of Open Standards, as defined by Ken Krechtmem.
"Open Use identifies the value of conformance for implementers and users. To the implementers, some means is required to assure that their implementation of a standard works as they intended. To support this level of conformance, a testing event may be held (sometimes termed a plug-fest) where multiple implementers gather to check their implementations with each other. For the user a simpler conformance indication may be all that is necessary. As example, in the European Union (EU), the CE marking is the manufacturer?s indication that the product meets the essential safety requirements of all relevant EU Directives. The CE marking indicating safety conformance reduces the user?s safety concerns.
Two levels of Open User are quantified:
1. Open Use via plug-fests or over the internet testing (implementer).
2. Open Use via identified conformance (user)." (http://www.csrstds.com/openstds.html)