Someone who believes that knowledge is not possible for themselves, some to different extents. They may believe that knowledge is possible, but paradoxically, it's impossible for them to know. While one will confine this to the metaphysical, most famously, regarding the existence of God, others will believe that they can know nothing at all, as not even their senses can be trusted.

Agnostics are often well-educated, and even more often do they see themselves as such. An agnostic, by virtue of their belief, typically sees themself as a very skeptical and critical person, and indeed, they usually are. They are often more intelligent on average than those who believe they know things, or at least, so the stereotype goes. Because of this, they often develop a sense of superiority, by which they can logically and rationally transcend the arguments of less-intelligent theists, who tend to be the most vocal ones.

An agnostic esteems above all else the scientific method. It is the infallible absolute of the agnostic. Everything must be empirically demonstrable to an agnostic, or it cannot be known to exist. A typical argument an atheist would use against a theist would be: "Since you cannot prove the existence of your God, how do you know that he exists?"

An agnostic attempts to apply empiricism to absolutely every aspect of reality. A thing does not exist unless it can be "scientifically proven". A modern understanding of science is the typical rhetoric of the agnostic.

An agnostic is a person who believes that the existence of a greater power, such as a god, cannot be proven or disproved; therefore an agnostic wallows in the complexity of the existence of higher beings.

Agnostics on religion (Christianity, Islam, Buddhists, etc): Religious zealots are often viewed as ignorant by agnostics’ because of their blind following of a supreme being which may or may not exist. Agnostics will often question the existence of a supreme power because a lot of modern religious beliefs have no basis in modern logic; therefore blind following of popular religions is viewed as an easy out for people who chose not to think for themselves.

Agnostics on atheism: On the other end of the spectrum, unlike atheists, an agnostic uses a more scientific approach to their belief system. An agnostic knows that just because there is no physical proof of the existence of a higher being, it dose not automatically mean that one does not exist. An agnostic views an atheist on the same plane as a religious zealot; often because the belief that human beings are the pinnacle of intelligence and there are few things that we do not or have the potential to understand.

The realization of knowing that “we cannot know everything” is the backbone of the agnostic belief.

Someone who is not arrogant enough to
think they KNOW whether God exists or not.

Someone who doesn't feel that their is enough evidence to prove or disprove god.

By strict definition, it means 'without knowledge', refering to deities. That is, an agnostic does not claim to have any definite knowledge of the existance of deities/a deity.

It is often said that agnosticism is a stepping stone to atheism. There is truth to this, as often the transition from theism to atheism is travelled through agnosticism. However, this is not the only form of agnosticism. Agnosticism can also develop as a rejection of both atheism and theism, for a number of reasons. All three discuss divinity in different ways, so it is foolish to say that agnosticism is simply a stepping stone to atheism, or undecided secularism.

One who believes that it is impossible to prove whether a supreme being (or a 'God') exists or not. An individualist who has finally realised that the statement 'Billions of mindless drones can't be wrong' is bull.

n. One who neither acknowledges nor refutes the existence of God

1. Strictly, someone who believes that it is impossible to know whether or not God exists. Note that they may still be either an atheist or a theist, they simply do not believe it is possible to prove beyond all doubt that God does or does not exist.
2. Someone who neither believes fully that God exists nor that s/he does not exist. This is the more common usage. Note that such a person can be neither an atheist or a theist.