Rootkit:

https://www.kaspersky.com/resource-center/definitions/what-is-rootkit?fbclid=IwAR1pcf0M8IXgf0gDK9iBWnr_CpjOhRbqw4UgdTLYxh1TlNse9n7P5mPq-5o

Antivirus:

https://www.verizon.com/info/definitions/antivirus/