app - abbreviation for application: a computer program that is designed for a particular purpose

https://dictionary.cambridge.org/dictionary/english/app

application - a program (such as a word processor or a spreadsheet) that performs a particular task or set of tasks

https://www.merriam-webster.com/dictionary/application

app - An app is a computer program that is written and designed for a specific purpose.

https://www.collinsdictionary.com/dictionary/english/app

etc. etc.