Interstitial is a generic term for referring to the space between other structures or objects. The word derives from the Latin interstitialis, literally "placed between", from inter, between, and sistere-stiti-statum, to place.
In crystallography, interstitial space refers to the open spaces within the crystal lattice.
In anatomy, interstitial cells are cells found in the spaces between organs and other tissues. Similarly, interstitial fluid is the fluid between organs and tissues, outside of the lymphatic or cardio vascular systems.
In television, interstitials refers to short programming which is often shown between movies or other events.
On the World Wide Web, interstitials are pages, such as advertisements or an age confirmation, that are displayed before an expected content page. Many people take issue with this form of online advertising.