Often I hear PMs (Project Managers) talk about feature and function. And I'm just so puzzled to differentiate them. Sometimes I think of a feature to be equivalent to a user story. Something like "As a user, Bob should be able to see a list of his payments", and they call it a feature. Sometimes it gets as big as a subsystem, something like "the ability to send SMS via web application". Function on the other hand sometimes gets as small as a task, "implementing digit grouping for number inputs", while there are cases when it gets as big as a whole CRUD operation.
My question is, how can we differentiate feature from function?