Infinite bafflement?

"Infinite baffle" is where the front wave emanating from a driver is completely separated from the back wave... as in, installing your woofer on the front wall of your house...

In real life, it usually means that the low freq driver is installed in a very large sealed cabinet -- large enough so that the pressure produced by the cone's movement produces an insignificant amount of noise compared to the actual music content.

is an elctrostatic speaker which is enclosureless an example of an infinite baffle speaker?

That's "open baffle"; sound emanates from both sides of the panel into the room. There are beneficial cancellations (front to back) but also loss of spl as the sound wave becomes too large for the baffle.
Dazz:

So a sealed cabinet performs in fact as an infinite baffle? ...with a sealed cabinet one has to do with resonances and standing waves within the cabinet...

Exactly. However, if the box is large enough to make the rear wave interaction less significant, there is a "simulation" of infinite baffle. As per Martykl & Shadorne, above.