A swedge is a bevel ground along the top of the blade near the tip, thinning the spine without sharpening it. It reduces the amount of steel behind the point so the knife penetrates more easily, and it is deliberately left blunt.
Most obviously on clip points, where the clipped section is usually swedged, and on spear points. Look at the top edge near the tip: if there is a distinct bevel there but it is not sharp, that is a swedge.
The words swedge and false edge are used for the same physical grind. In careful usage a swedge is never sharpened and a false edge may be.
Less steel behind the point means the tip enters material with less force. It also removes weight from the front of the blade, shifting balance back toward the hand.
The cost is tip strength. A heavily swedged tip has less material to resist bending, so it is the wrong choice if you expect to lever with the point.
None required. The swedge is on the spine side and never touches your stone.
If a listing describes a sharpened false edge, that is a different thing, and a blade sharpened on both sides is described differently under some local ordinances.