Let us take a real-time scenario:
Tenant - In our project, we are working on different SAP Modules viz., SCM/P2P, CRM/O2C, FI, BI/BW, PI. So when automating their tasks, we need to segregate their data so that each team can see their respective automated tasks in their corresponding Orchestrator Tenants. But we have to keep in mind that the underlying database for storing their data will be same (MS Azure, Amazon cloud, etc.,)
Unit - Unit is more like system/database access. Unit is generally used for restricting users to use some options in the orchestrator. For example Admin will have access to all the unit, whereas a monitoring resource can be restricted to create robots, processes, etc., in the specified orchestrator tenant. Likewise you can add ‘n’ number of users in a tenant and provide various access levels (in our case, Units) to them.
Hope you understood now, if not please reply your doubt. I’m always delighted to solve the queries which makes me to explore a lot alongside you. You’re always welcome to post your queries in the forum.