Customer Tags

Use this section to classify your customers. When creating a profile for a customer, you can specify their type as a formal customer, a family customer, a corporate customer, etc. You can also make these tags mandatory and if you do this without the customer tag, a customer profile can not be saved.

To make it mandatory or optional go to setup->preferences->customer prefs.

Go to Setup, then Sales Setup, and then Customer Tags.

Add the tag name and submit.