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Nothing

Nothing is a concept that describes the lack or absence of anything at all. Colloquially, the concept is often used to indicate the lack of anything relevant or significant, or to describe a particularly unimpressive thing, event, or object. It is contrasted with something and everything.

In mathematics, nothing does not have a technical meaning. It could be said that a set contains "nothing" if and only if it is the empty set, in which case its cardinality (or size) is zero. In other words, the word "nothing" is an informal term for an empty set. However, since two minus two is also called nothing, it could also refer to the number zero.

In physics, the word nothing is not used in any technical sense. A region of space is called a vacuum if it does not contain any matter. But it can contain physical fields. In fact, it is practically impossible to construct a region of space which contains no matter or fields, since gravity cannot be blocked and all objects at a non-zero temperature radiate electromagnetically. However, supposing such a region existed, it would still not be "nothing", since it has properties and a measurable existence as part of the quantum-mechanical vacuum. The only physical concept in which the literal meaning of nothing can be embodied, is with the theoretical probability over the existence of Dark Matter; a collective substance which is referred to as being an anti-matter and having no mass - it is a concept principally used to explain the unusually high, regarding the mass of visible matter, mass of the universe.

In computing, "Nothing" (VB.Net), or "null" (Java, C#, others), can be a keyword used to represent an unassigned variable, or a pointer that does not point to any particular memory address, or a reference that does not refer to an extant object. Similarly, Null is used in SQL as a symbolic representation of the absence of data. This meta-data usage of "null" is different from the unprintable ASCII and unicode null character, which has a numerical value of zero — although it is different from the ASCII character for zero ("0"). The ASCII blank character (" ") is not the same as an empty string (""), which is itself sometimes confused with the null pointer in languages such as C. Most forms of assembly language have a no-operation (nop) instruction (often with a numerical value of zero) — that is, a command to do nothing, which can prove useful for blanking out areas of problem code.

Source: http://en.wikipedia.org/wiki/Nothing