In japanese, expression showing the full satisfaction obtained by eating, drinking or tasting anyway, somethings really delicious (delicious is what oishii properly means), mostly, but not necessarily, related to
food or drink.
Coming from the Imperial Family and the noble class of the Heian period (794-1185
AC), it's still mainly used among highly educated
people and academic circles, as a way of very polite and formal appreciation, sometimes just in order to
mark the intellectual superiority from the common way of speaking.