Infinite bafflement?

Hartley woofers (18"/24"woofers) used to recommend mounting their woofers in crawl-space openings/infinite baffle.Where the large crawl-space was the "cabinet" and never reflected to effect the front waveform.

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.

Ojgalli's explanation is a good one. It all has to do with the relationship of the compliance of the driver and that of the air in the box.

In layman's terms, a sealed box can be either acoustic suspension (AS) or infinite baffle (IB). A small box, with a very compliant suspension will tend to be AS, a larger box and/or less compliant driver will tend to be IB.

By the way, AS is truly one of the landmark developments in the history of audio. In my mind, nothing has eclipsed it, and is probably the biggest reason we have 2 channel (as opposed to 1) audio.