On Collect, device means the phone or tablet your data collectors would be using to collect responses. A device points to a data collector.
A device is a phone or tablet that you can use to collect responses once you have created a form. Devices are generally synonymous with your surveyors or data collectors. Once a form is published, you can give access to multiple devices which can then use the Collect mobile app to collect responses and fill in the form.
Active Devices:
During your data collection, a device will be said to be active if it has been used to collect at least one response during the subscription period.
Next Step:
If you are looking to add a data collector or Collect, check out this guide: Adding devices or data collectors on Collect.