Similar to in Salesforce, a field type where once you enter a value it gets added to a Picklist for that field. -- Next time you start typing that value in that same field, it auto-suggests based off what you're typing.

Use case, a "Referred By" field. - When someone refers a client, I put their name into Referred By field on the new client. But by their 10th referral, I don't want to keep manually typing their name out, I'd like for this field to auto-suggest past Referrers that I've previously entered.