A Trusted Device can be used if you have 2-Factor Authentication enabled. If you sign in on a trusted device, you will not be prompted to enter your 2FA code. A trusted device is any computer, phone or tablet that isn't shared amongst other people and you trust is secure.
Add a Trusted Device
If you haven't already added your current device, you can add it as a Trusted Device from the settings page. There will be a blue box with an identifier for the current device and a green + Add Device button. Click on that button to add the device.
Add a device from Trusted Device settings
Another option is to add your device when entering your 2FA code while logging into your account. Simply check the Trust this device? checkbox under the 2FA 6-digit code entry field.
Add a device from 2FA prompt
Trusted Device List
If you have already set up a trusted device, a table on the Trusted Devices page will list the currently enabled devices. The table shows the Device Identifier - the operating system and browser identifier, Last tested - when the device was last used to log in, Added on - when the device was added as a trusted device. You can also click on the red icon to delete a trusted device.