Nothing

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: This is only scratching the surface, more examples can be found at this category page.
 * 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