DifferAnce is an anglo-saxonized version of the french word for differance which, I'm told, sounds like the word "difference" in French, but is spelled differently.  I wanted a way to make this term conspicuously different from difference and easy to type, so I have used a capital A in the middle of the word.  In published writings, I, and others, sometimes use differance.  The exact way to write this term in English, however, has not been entirely established.  At any rate, "differAnce" is a term that Derrida coined.  Derrida also is responsibility for the popularity of the word "deconstruction' in our postmodern vocabularly.  "Deconstruction", however, is  a term he harvested from a little known use of the word "deconstruction" in Heidegger. 

What follows is is me quoting Derrida and reflecting on his term differAnce in my paper that has recently been called the "Pomo Primer".  It is referenced at the end of this note. 

       The word "differAnce", spelled with an "a",  is a coined 
       term, and Derrida contrasts it with the vernacular term 
       "difference".  Patterns of "Difference," he explains, [are ] 
       ...'produced' - deferred -- by 'differance'" (Derrida, 1982, 
        p.14).  But what does this mean?  That difference is deferred 
        by differAnce? 

       Imagine observing a quilt on the wall with patches of yellow, 
       blue and white.  If you notice the yellow and the non-yellow, 
       you see a pattern of concentric boxes.  If you notice the 
       blue and the non-blue you see a checkered design.  Each 
       pattern is a play of differences, but it is a different set 
       of differences when yellow is differentiated from non-yellow 
       than when blue is differentiated from non-blue, a different 
       set of differences that shows us different patterns. 

       What is interesting about this shift from one pattern to 
       the other is that it not only calls our attention to a 
       new pattern, but that it suppresses our awareness of the 
       other pattern.  DifferAnce, defers a pattern of differences 
       (say the pattern of differences between the blue and the 
       not-blue).  That is, one pattern of differences pushes 
       into the background another possible play of patterns. 
       You cannot study the pattern of yellows and the pattern 
       of blues at the same time because differAnce causes 
       one or the other patterns to be "deferred".  DifferAnce 
       is the hidden way of seeing things that is deferred 
       out of awareness by our distraction with the imagery 
       that captures our attention.  Because it contains this 
       other way to see things "DifferAnce is the...formation of 
       form."(Derrida, 1976, p.63).  It is the "historical 
       and epochal 'unfolding' of Being..."(Derrida, 1982, 22). 

DifferAnce might be related gestalt switch in looking at an ambiguous picture.  It is, on the one hand, what is pushed to the background, the pattern created by the blue and white, say, and it is also what is able to push the other pattern into the background.  It is what causes one or the other pattern to be deferred. 

from: 

Shawver, L. (1996).  What Postmodernism Can Do for Psychoanalysis: A Guide to the Postmodern Vision.  The American Journal of Psychoanalysis, 56(4), pp.371-394. 

Derrida, J. (1976). Grammatology. Baltimore: The Johns Hopkins 
   Press. 

Derrida, J. (1982a). Differance.  In J. Derrida (Ed.), Margins of 
   Philosophy, pp. 3-27. Chicago:  The University of Chicago Press.