Manuscript language material:

The manuscript language material category is applied to items for language material in handwriting, typescript, or computer printout including printed materials completed by hand or by keyboard.  At the time it is created, this material is usually intended, either implicitly or explicitly, to exist as a single instance.  Examples include marked or corrected galley and page proofs, manuscript books, legal papers, and unpublished theses and dissertations.

Code t in Leader/06 indicates that the content of the record is for manuscript language material or a microform of manuscript language material.