The term "teaching portfolio" means different things to different people. For some, it means simply a loose file of teaching materials. For others, it's a more carefully organized document. In his chapter on "Evaluating Teaching Through Portfolios" in Peter Seldin's book Changing Practices in Evaluating Teaching, John Zubizarreta defines it this way:
[A teaching portfolio] is an evidence-based written document in which a faculty member strategically organizes concise, selective details of current teaching accomplishment and uses such information for documentation of performance but more significantly for reflective analysis and peer collaboration leading to improvement of teaching and student learning (164).
Much has been written about teaching portfolios--how to compile them, how to organize them, how to evaluate them. Some good resources are the following:
Nancy Chism, Peer Review of Teaching: A Sourcebook. Bolton, MA: Anker, 1999 (108-123).
Peter Seldin, The Teaching Portfolio: A Practical Guide to Improved Performance and Promotion/Tenure Decisions, 2nd ed. (Boston: Anker Publishing, 1997).
John Zubizarreta, "Evaluating Teaching Through Portfolios," in Changing Practices in Teaching Evaluation, ed. Peter Seldin. Bolton, MA: Anker, 1999 (162-182).