A hardware/software system implemented to satisfy a particular set of requirements. In this context, an application incorporates a system used to satisfy a subset of requirements related to the verification or identification of an end user’s identity so that the end user’s identifier can be used to facilitate the end user’s interaction with the system.
Sources:
FIPS 201-3 under Application

  A software program hosted by an information system.
Sources:
CNSSI 4009-2015
NIST SP 1800-16B under Application from NIST SP 800-137
NIST SP 1800-16C under Application from NIST SP 800-137
NIST SP 1800-16D under Application from NIST SP 800-137
NIST SP 800-137 under Application
NIST SP 800-37 Rev. 2
NIST SP 800-53 Rev. 5 from NIST SP 800-37 Rev. 2
NISTIR 7621 Rev. 1 under Application from CNSSI 4009-2015

  the system, functional area, or problem to which information technology isapplied. The application includes related manual procedures as well as automated procedures. Payroll, accounting, and management information systems are examples of applications.
Sources:
NIST SP 800-16 under Application

  The system, functional area, or problem to which information technology is applied. The application includes related manual procedures as well as automated procedures. Payroll, accounting, and management information systems are examples of applications.
Sources:
NIST SP 1800-16B under Application from NIST SP 800-16
NIST SP 1800-16C under Application from NIST SP 800-16
NIST SP 1800-16D under Application from NIST SP 800-16

  A system for collecting, saving, processing, and presenting data by means of a computer. The term application is generally used when referring to a component of software that can be executed. The terms application and software application are often used synonymously.
Sources:
NISTIR 7695 under Application from ISO/IEC 19770-2 - Adapted