marker 1. Small amount of an easily detected substance that can be used to follow and quantify the flow of materials or movement of organisms not otherwise visible or detectable by ordinary means. 2. An isotope of an element, a small amount of which may be incorporated into a sample of material in order to follow the course of that element through a chemical, biological, or physical process, and thus also follow the larger sample. The tracer may be radioactive, in which case observations are made by measuring the radioactivity
pushpin(A user-applied location marker that can be annotated and saved to a collection); leaderboard(List of the top players in a game or other competition on Xbox Live); bookmark(A location or selection of text in a file that you name for reference purposes. Bookmarks identify a location within your file that you can later refer or link to)
