Nothing: not anything; not one single thing.
The definition of nothing is literally just a rephrasing of the word we were trying to define. So, what is nothing? Everything is something, right?
For this, I made theories:
1) Nothing is impossible. See, everything is made up of particles and atoms, including air. Air is a mixture of elements. So, if air were "nothing", the elements that make up air as well as the whole periodic table would be nothing as well.
2) Nothing is un-existence. I found this one surprisingly hard to describe, so I made a small story:
Amy was walking home to school one day with her friend Rory. (Anyone see what I did there) They were talking about maths and such, when suddenly, Amy was gone. Disappeared. Amy didn't exist anymore, at least to the human eye, so Amy is nothing.
3) Nothing is fake. It is something we humans made up, like Santa. Nothing is nothing, so nothing can't be.
4) Thank you Parsavegely for this idea. :)
Nothingness. it's the absence of things, no? In a state of nothingness, you wouldn't have velocity. On the other hand, there would be no stationary-ness. Same goes with weight. And since that isn't possible, the universe AND all matter wouldn't exist had there been a state of nothingness, and if there was a state of nothingness, there must be no nothingness, so nothingness can't happen.
Nothingness isn't real.
5. (I won't lie my head exploded when came up with this one.) Nothingness is everything. The electronic you are using to read this chapter on, where you live, even you are a small pocket of nothingness inside an infinity of nothingness.
6. Maybe nothingness is just a surreal figment of imagination to help us describe the feelings and the textures that would be seemingly indescribable to describe without this "nothing" word.(Like, describing the taste of water. I couldn't. Comment what you think it tastes like if you can - and no, "it tastes like water" or "nothing" is not correct.)
7. (Last but not least :)) The gaps between atoms and their subatomic particles, nuclei, gaps between the atoms themselves. There is absolutely nothing in between those gaps, correct? Surely if there was no definition of "nothing" then all atoms would collide and create atomic explosions and utmost apocalyptic destruction. So, in other words, there is a definition of nothing in the sense of infinitely smaller than microscopical science. So really there IS a definition of nothing, speaking in atomic science, but in a humanely, geographically, physically, and mentally scientific way, there is NO SUCH thing as nothing.
So what theory do you guys like? Sorry for being so boring XD