Here is the way I like to think about a feature:
Small, client-valued bit of functionality. For example, “Hide data from non-admin user view if the data represents a ‘sensitive value.'”
If the paragraph of text describing the feature is clear enough:
- the developer can estimate the time required to implement the feature.
- the tester can write an acceptance test to prove the feature exists and is working properly.
If the estimate or the test can’t be made due to lack of detail, then ask for more explanation about the feature.