Five zero-days patched by Apple this year
https://www.bleepingcomputer.com/news/security/apple-emergency-update-fixes-zero-days-used-to-hack-iphones-macs/
Apple has released security updates on Thursday to address two zero-day vulnerabilities exploited by attackers to hack iPhones, iPads, and Macs.
Zero-day security bugs are flaws the software vendor is unaware of and hasn't patched. In some cases, they also have publicly available proof-of-concept exploits or may be actively exploited in the wild.