As indicated by the IEEE definition, this might be a software design document or program source code, but use cases, business process definitions, test case specifications, and a variety of other technical documentation may also be walked through.
A walkthrough differs from software technical reviews in its openness of structure and its objective of familiarization.
It differs from software inspection in its ability to suggest direct alterations to the product reviewed.
A walkthrough may be quite informal, or may follow the process detailed in IEEE 1028 and outlined in the article on software reviews.
Any combination of interested or technically qualified personnel (from within or outside the project) may be included as seems appropriate.