Stropping is the term used to polish or otherwise finalize the edge on a razor blade. To establish an edge or repair an edge requires honing, but most razors can be maintained quite a few times with a strop before having to take them out of commission.
In theory stropping can be done on human skin, and some pioneers maintained their razors by swiping them back and forth across their own forearm. I have a nice scar from trying that trick, so I don't recommend it.
What one does use is a strop, which is typically two strips - one of belt-like leather, and the other linen with a bit of "tooth", held together at one end with a nut and bolt attached to a clip which clips onto a hook or eyelet screwed into a wall or dresser. The other end has some kind of handle, which is held in the non-dominant hand of the stropper.
You pull the strip taut, using the linen side first. Holding the linen belt under tension, you put the straight razor flat on the surface of the strop, with the bottom part of the razor (closest to the handle) flush with the top edge of the strop. Dragging the blade down the strop with the sharp side opposite to the direction of travel, you also pull the blade across the belt as you go so that by the end of the stroke the top end of the belt is flush with the top end of the razor. To be very, very clear. You are not "slicing" the belt, it's the blunt side that leads. Apply no pressure but keep the sharp blade edge in contact with the strop at all times.
Once you've reached the end of the stroke, roll the blade over the blunt side so it's facing the other way, and line it up again with the bottom edge of the razor flush with the top edge of the strop. Drag it back across the strop, bringing the blade across the strop as you do so. If you mime the motion with your dominant hand, it's like drawing an elongated X. Repeat 10-15 times.
Flip the strop over to the leather side and repeat the motions again the same way, giving it about 20 times. What this does is knock off microscopic damages and imperfections and re-sharpens the very edge to a mirror finish. Done properly, it will maintain the edge on a razor for quite some time.
Watching someone adept at this is hypnotic, seeing them perfectly sweep the blade back and forth, constantly maintaining the critical and important tension. Applying pressure or slackening the strop changes the angle at which the blade rests on the surface and will ruin the blade geometry, so get the motion right before getting it quick. But with some practice you'll be absentmindedly swiping it quite quickly, and efficiently.
If this doesn't re-sharpen the blade, the blade has worn down to the point at which it needs to be honed with a stone or series of stones before being stropped again.