Resources are a specific type of card or token which grants it's owner the ability to do something that they wouldn't be able to without them. The main differentiator between resources and alternate scoring is that resources are not tracked on a Scoresheet. This can either be because a house rule states that a certain type of card cannot be played without owning the proper resource card for it, such as only being able to play Cake cards if you control "Baker's Mountain", or because a card states that it requires a resource to be spent when played, such as a strange rock which requires 3 strange energy to be played which is produced by the "Strange Generator". In the latter case, strange energy evaporates if it is produced but not spend by the end of the turn.
In general, if it exists long term it's alternate scoring, if it exists short term it's a resource, and if it says on the field to grant access to restricted cards it's also a resource.