Greene is putting me on the spot here! :smily:
Aeriel roots are simply roots that develop along a stem above the ground. Most commonly in nature, they grow long enough to attach to nearby moist ground or tree bark to help support the plant while it climbs. Monstera deliciosa is the best houseplant example of this phenomenon. For potted plants, they generally serve no purpose and can be cut off.
The roots that are shown here on the Pothos and Marginata, I would describe as incipient roots rather than aerial roots. Incipient roots form at stem nodes in anticipation of being exposed to moisture so they can develop more fully. Absent very humid air or contact with damp substances, they remain incipient or undeveloped. In a way, any stem node is a less prominent incipient root waiting for the right conditions (moisture) to trigger further growth and propagation.
When put in water or damp potting soil, those little bumps or nodes start to grow and become fully fledged roots.
I hope I haven't made this too complicated. If so, blame Greene!