Uncertainty - A lack of understanding and awareness of issues, events, path to follow, or solutions to pursue. 

Unit Price – The cost per unit of the commodity or service (e.g. per ton, per labor hour, or per foot).

Use Case - An artifact for describing and exploring how a user interacts with a system to achieve a specific goal.

User Story - A brief description of an outcome for a specific user, which is a promise for a conversation to clarify details.

User acceptance testing (UAT) - The final stage in software development during which software is tested in real world environment to access its functionality.