What does PhD stand for? Is it academically correct to use "Ph.D.(c)"
after your name to indicate you are enrolled but not yet completed
your degree as used in this site
http://www.nlp.com/about-nlp/index2.html

What is the av length of time to complete a PhD and how long is the
thesis on average?

Hello.

Here's a good description from Purdue University of what a Ph.D is:

"A Doctor of Philosophy degree, abbreviated Ph.D., is the highest
academic degree anyone can earn. Because earning a Ph.D. requires
extended study and intense intellectual effort, less than one percent
of the population attains the degree. Society shows respect for a
person who holds a Ph.D. by addressing them with the title 'Doctor.' 
To earn a Ph.D., one must accomplish two things. First, one must
master a specific subject completely. Second, one must extend the body
of knowledge about that subject. "
source: Notes On The PhD Degree, hosted by Purdue
http://www.cs.purdue.edu/homes/dec/essay.phd.html


Yes, Ph.D. (c) is a common and legitimate way of identifying someone
who is a Ph.D Candidate (i.e., someone who is in the final stages of
completing a Ph.D.)

Here's an explanation from St Louis University:
"A student who has been advanced to candidacy is entitled to identify
him/herself as PhD(c)."
source: Slu.edu
http://www.slu.edu/colleges/NR/phd2_dissertation.html

Here's an explanation from University of California San Diego:
" After completing the qualifying exam, you can apply for a 'Candidate
of Philosophy degree (PhD.C.). '"
http://ece-classweb.ucsd.edu/gsc/info/latetips.html

Here's an example listed on the web site of the American Medical
Association:
"Karen E. Geraghty, PhD (c) 
...she is completing a PhD in the history of medicine at the
University of Chicago..."
source: ama-assn.org
http://www.ama-assn.org/ama/pub/article/7373-2990.html

More examples:

"Theresa Ann Yeo, PhD(c)...
PhD Candidate, Johns Hopkins University, Bloomberg School of Public
Health"
source: Johns Hopkins University
http://www.son.jhmi.edu/directory/faculty/faculty_detail.asp?ID=652

"KIM MCCLANE, Ph.D.(c)...
Currently she is completing her dissertation at the University of San
Diego for her Doctorate of Nursing Sciences.
Source: csudh.edu
http://www.csudh.edu/soh/don/faculty/kmcclane.htm


The median length of time a student is enrolled in graduate school to
complete a Ph.D. is 7.4 years.
source:
University of Chicago's Doctorate Recipients from United States
Universities: Summary 2000
http://www.norc.uchicago.edu/issues/sed-2000.pdf


As for the length of a thesis (also sometimes called a
"dissertation"), estimates vary:

"A finished dissertation is generally 200-300 pages long. "
Source: Harvard University
http://www.fas.harvard.edu/~rll/graduate/prospectus.html

"There is no fixed length for a dissertation, but most are between 150
and 200 pages long. "
Source: University of Nebraska - Lincoln
http://www.unl.edu/modlang/grad/french_PHD.html

"a doctoral dissertation--usually at least 200 pages long"
http://www.history.ku.edu/Graduate%20Program%20Folder/Graduate%20Fields/Graduate%20American%20History.htm

search strategies:
"phd is", doctor philosophy
"phd c", candidate, completing
phd, "years to complete"
dissertation, "pages long"

I hope this helps.

Excellent! Thanks :)

Doctor of Philosophy.  Cambridge uses D. Phil for the same thing.
No, I dont think you can use it as you have suggested.  Use your
higest completed qualification, say MA.(hons) or whatever.

2years min - 3 yerars average - whatever max.

from 150 pages up, including refs.

I feel that I need to justify my comment in light of the excellent
answer provided above.

Re duration: where I am, you enrol in a PhD *after* completing an
honours degree, so you already have 2 years of PG work behind you. 
Even so, it looks like where you are it usually takes longer.

PhD(c) is a new one on me.  Still, it seems that simply being enroled
is not sufficient to grant this privilege, and passing some exam, or
being accepted for candidature is required after enrolment.

I guess there is variability among schools and countries.