Lars Wirzenius#Subplot is a tool for documenting acceptance criteria and how they are verified. We want to use clear terminology. We've reached an internal consensus, posted in a thread below, and would like to hear what others think.
A "need" is a vague, high level description of what the system should be like. This is used as input to drive "acceptance criteria", which are clear, unambiguous, and specific, and come with a specified way to verify they are met. These in turn inform "requirements", which are used to drive development and automate testing.
In Subplot, acceptance criteria are verified using "scenarios", from which code is generated. Further, the intent is that both acceptance criteria and scenarios are understood by relevant stakeholders.