transparent
1. <jargon> Not visible, hidden; said of a system which functions in a manner not evident to the user. For example, the Domain Name System transparently resolves a fully qualified domain name into an IP address without the user being aware of it.
Compare this to what Donald Norman calls "invisibility", which he illustrates from the user's point of view:
"You use computers when you use many modern automobiles, microwave ovens, games, CD players and calculators. You don't notice the computer because you think of yourself as doing the task, not as using the computer." ["The Design of Everyday Things", New York, Doubleday, 1989, p. 185].
2. <theory> Fully defined, known, predictable; said of a sub-system in which matters generally subject to volition or stochastic state change have been chosen, measured, or determined by the environment. Thus for transparent systems, output is a known function of the inputs, and users can both predict the behaviour and depend upon it.