Since it seems to have helped some folks, here is the way I defined "#serverless" to a group of workshop participants at @ServerlessConf this week. 
Note that a technology can use parts of the programming model (kubeless/knative/etc) or the operational model (say, RDS SQL Server), but you only get the full benefits of serverless if you are in the center of the diagram.
As a side question, is there such a thing as a usage-priced service (you pay only for the network/storage/compute resources you actually consume) that is not also fully managed (you have infrastructure responsibilities)? I couldn't think of one.
