Add widget definition to the terminology table

What does this MR do and why?

Describe in detail what your merge request does and why.

Adds a definition for widgets in the context of work items.

Adds more context about what widgets are.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.