Nothing. The absence of anything, as the name says ("no thing").
However, what a thing is, depends on context. This means that nothing has a variety of definitions, which commonly are:
- Air
- Zero or 0
- A void
- A set with no members, and no subsets other than itself (denoted as ∅, {}, or literally "null")
- A lack of useful properties or definitions
- Imaginary or impossible
This is only scratching the surface, more examples can be found at this category page.
