1.
Source:
Bibliographic Formats and Standards, 2nd ed., OCLC.
<Fixed-Field Elements: Cont = Nature of Contents: http://www.oclc.org/oclc/bib/cont.htm>

Technical reports. The item contains technical report material. This is an item that is the result of
scientific investigation or technical development, testing, or evaluation, presented in a form suitable
for dissemination to the technical community.

2.
Source:
Bibliographic Formats and Standards, 2nd ed., OCLC.
<Special Cataloging Guidelines, Chapter 3.3 Technical Reports: http://www.oclc.org/oclc/bib/3_3.htm>

According to ANSI Z39.23 (1983),

     . . . a technical report is a document that gives the result of research or developmental investigations,
    or both, or other technical studies. . . A technical report is initially submitted to the person or body
    for which the investigation was carried out or by which it was sponsored. Copies of it may
    subsequently be made available in limited quantities. . . , but these copies are not produced
    commercially and are not available from booksellers or other commercial sources. . . .
    Technical reports are usually published irregularly, either in series or as separate monographs.
    Technical reports are not typeset but are reproduced from typescript by near-print processes, and
    they are usually concerned with only one specific subject or with a few closely related subjects.
 

3.
Source:
Harrod, Leonard M.  The librarians' glossary of terms used in librarianship and the book
crafts and reference book.  3rd ed., 1971.

Technical report.  A scientific paper, article, translation, probably recording the current position
of scientific research and developments, etc., whether security classified, unclassified or declassified.