Input variables allow you to set variables that may change between runs. You can access them by opening a flow's settings:
For example, if you create a flow that scrapes all the tweets from a particular profile, you can create an input variable for the username so that it can be changed between runs.
The "Clear value when flow is shared" option ensures that any sensitive information will be removed when you share a flow.
Once you've created an input variable, you can reference it in your flow to customize the behavior:
Once created, input variables allow you to easily change variables between runs by setting values in the Run tab: