Definition

In terms of Oracle Cloud Infrastructure (OCI), a tenancy is a secure and isolated partition within OCI, where you can create, organize, and administer your cloud services.

Real world example

You book an Airbnb stay, and you receive the keys to the space you booked. That is your secure and isolated area within the premises, where you cook your meals, watch Netflix, do your work, go out and come back in, and sleep. No one else can enter your space, use your amenities, or see what you're doing inside.