What is t minus 15?

"T minus 15" typically refers to a countdown where "t" represents a specific event or time, and "15" indicates 15 units of time before that event occurs. For example, if "t" is set at launch time, then "t minus 15" means 15 seconds (or minutes, depending on context) before the launch. It is commonly used in contexts like space missions or project timelines to denote the time remaining until an important event.