A type of exploit (Remote Code Execution) that can be used to secretly infect your device with spyware without requiring any interaction from you (0-click).

Pegasus [0] and the like — commercial spyware updated with the latest exploit chains, developed in-house or purchased from markets like Zerodium, sold as terrorism-prevention tools to such trustworthy states as Russia, UAE, and Hungary.

[0] https://en.wikipedia.org/wiki/Pegasus_(spyware)