A flow is an automation tool that allows you to create processes that perform actions based on user input or record changes. A flow can be triggered by a user who launches it from a button, link, or Lightning page, or by the system when a record is created or updated. A flow has different versions that can be active or inactive.
An active version is the one that runs when the flow is triggered, while an inactive version is the one that is saved but not running. When you deploy a flow to production with a change set, the flow version is deployed as inactive by default. This means that you need to activate the flow manually after deployment if you want it to run in production. References: https://help.salesforce.com/s/articleView?id=sf.flow_overview.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.flow_distribute_changesets.htm&type=5