|Definition - When a preposition in a sentence appears to have no object.|
Example - This is the place I told you about.
(In the above, the preposition about is stranded.)
1. You really should mention that preposition stranding is in fact the norm in English, except among die-hard, ossified prescriptivists. The preposition only "appears" not to have an object. If you added the word it after the preposition — as in
"This is the place I told you about (it)"
— it becomes quite apparent that there are two objects.