For the purposes of this page, "canon" is probably best represented by Merriam-Webster's definitions '''3 b''' the authentic works of a writer and '''3 c''' a sanctioned or accepted group or body of related works.
There are a number of different "levels" of canon sometimes considered when discussing the Klingon language. Absolutely Canonical Star Trek: that which is shown on screen. Mostly Canonical Star Trek: that which is published in reference books written by the same people who are responsible for what is shown on screen. Canonical tlhIngan Hol: that which is written (or sometimes merely spoken) by Marc Okrand, listed here as canonical sources.
Some people contend that anything coming from Paramount is just as reliable a source as is Marc Okrand for the purposes of Klingon language. Others make a clear distinction between tlhIngan Hol and Paramount Hol.
There are also subtle differences among individuals in determining exactly "how canonical" certain interpretations of Marc Okrand's writings are. There are people who firmly believe in particular theories of how the Klingon language should work, and who can often twist the known examples to support those theories, while others can use the same examples to support contrary theories. Sometimes clear examples of usage are absent, and divergent extrapolations are possible. In decreasing order of usefulness, one might say "canon says", "canon shows", "canon supports", or "canon is consistent with".