Wiktionary
n. (context physics English) spacetime viewed on a quantum level, i.e. as a "foam" of randomly appearing and disappearing Planck scale wormhole (black hole and white hole).
Wikipedia
Quantum foam (also referred to as space-time foam) is a concept in quantum mechanics devised by John Wheeler in 1955. The foam is supposed to be conceptualized as the foundation of the fabric of the universe.
Usage examples of "quantum foam".
On the very tiny length scale of the quantum world, known as the Planck length (around 10-35 metres), spacetime is thought to be a quantum foam - a perpetually changing mass of tiny wormholes.
There have even been experiments in downloading human minds into the quantum foam.
The fundamental building blocks of Creation had nothing to do with quantum foam any more than they did with plant sap.
In effect, you're a large virtual particle that has tunneled out of the quantum foam.
Standing before the sink in the tiny kitchen alcove of his quarters on Deep Space 9, Sisko whisked at the eggs in their copper bowl, smearing out the streaks of dark pepper sauce, frothing the egg mixture into a whirlpool just as the wormhole frothed the quantum foam of normal space-time.
After zapping through the whole thing faster even than Driver, he'd come out raving and raring to go, hand-waving wild speculative explanations of the implied AG physics, from which all I could extract was that the density of the transplutonic nuclei generated a quark-gluon plasma at the nuclear core which, when set in cyclical motion, interacted directly with the quantum foam of the space-time manifold, after which matters got complicated and arcane.