Wiktionary
n. 1 A cap placed on the end of something 2 A product display at the end of a supermarket aisle
Wikipedia
In retail marketing, an endcap is a display for a product placed at the end of an aisle. It is perceived to give a brand a competitive advantage. It is often available for lease to a manufacturer in a retail environment. Products placed on an endcap for sale will sell at a much faster pace than products not on the endcap. The display of products on the endcap is sometimes also called a feature.
Usage examples of "endcap".
I flick off its endcaps with my thumbnail as I raise it to peer through the eyepiece.
They swept across the sky, heading towards the northern endcap, already several hundred metres long, twisting round the lighting tube like bloated contrails from an acrobatic display team.