Real-Time Application (RTA) is an application program that functions within a time frame that the user senses as immediate or current. The latency must be less than a defined value, usually measured in seconds. Whether a given application qualifies as an RTA depends on the Worst-Case Execution Time (WCET), the maximum length of time a defined task or set of tasks requires on a given hardware platform. The use of RTAs is called real-time computing (RTC).
Source: https://www.techtarget.com/searchunifiedcommunications/definition/real-time-application-RTA