"Differance"
Derrida introduced Differance (notice the a instead of e) as a concept of creating differences over time. It is temporal.
While TL;DRs are good in the short term and nice to know, and will get us some nerd points in society, to understand the importance of this concept, one has to not only read this 24-page essay, but also a substantial part of the materials mentioned there.
So, on one hand, we have our plain, old difference. We use it all the time. This means two entities are not the same. But, this newly introduced differance is the process that works in our world over time and creates the differences, often of the same thing.
It is important to understand that differance doesn't exist, we can only see differences made by it. We cannot even bring it into existence because that will actually dissolve it.
This also means that it is not how God has been defined in the negative theology.
Now, let's think about why this concept is important or interesting. First, let's consider this passage:
It means our knowledge about this world, all the categorisations we have in our head, so that we can distinguish this or that, is not based on our comprehensive knowledge of things. Instead, we know too little, but we know the differences between things. So, you can imagine that our reality is a big block of marble and we see it being chiselled away bit by bit, acknowledging differences, we get to know the ontological categories. These differences are the defining factors of the world.
Differance is that process of chiselling, over time.
Differance is also the driving force for Dasein— a temporal phenomenon. It doesn't exist at a point in time, but over a stretch of time, ever changing, ever interacting. It is the tapestry of ever-accumulating traces created by differance, which often has the illusion of being only at present.
Coming back to the signs, the signs we use in our languages are placeholders for things that are not present. This act of signification itself depends on differance because with this sign, we are deferring the entity we are signifying. Maybe we haven't stumbled upon languages and found a nice tool to use. Languages, perhaps, have a deeper ontological root, which makes it necessary for sentient beings, which brings us to the closing thought of this essay:
Being
speaks
through every language;
everywhere and always.