It has been argued that Agnosticism is a belief system.
Definition of Agnostic:
Agnosticism is a concept, not a religion. It is a belief related to the existence or non-existence of God.
An agnostic is a person who feels that God's existence can neither be proved nor disproved, on the basis of current evidence. Agnostics note that some theologians and philosophers have tried to to prove, for millennia, that God exists. Others have attempted to prove that God does not exist. Neither side has convincingly succeeded at their task.
Are they Theists? No, because Agnostics do not believe in a God, or a Goddess, or in multiple Gods, or multiple Goddesses or in a pantheon of Gods and Goddesses.
However, some Agnostics consider themselves to be Atheists. That is because the term "Atheist" has two slightly different meanings:
1. A person who positively believes that no God(s) or Goddess(es) exists. E. Haldeman-Julius suggests that "The atheist perceives that history, in every branch of science, in the plainly observable realities of life and in the processes of common sense there is no place for the picture of a God; the idea doesn't fit in with a calmly reasoned and realistic view of life. The atheist, therefore denies the assumptions of theism because they are mere assumptions and are not proved; whereas the contrary evidences, against the idea of theism, are overwhelming."
This is the definition of Atheism used by most Christians, other Theists, and dictionaries of the English language.
2. A person who has no belief in a God or Goddess. Just as a newborn has no concept of a deity, some adults also have no such belief. The term "Atheist" is derived from the Greek words "a" which means "without" and "Theos" which means "God." A person can be a non-Theist by simply lacking a belief in God without actively denying God's existence. This is the definition of Atheism used by most Atheists.
Some Agnostics feel that their beliefs match the second definition, and thus consider themselves to be both Atheist and an Agnostic. Such confusion is common in the field of religion. We have found 17 definitions for the term "Witch," eight for "cult," and six for the "Pagan." -- all different. A lack of clear, unambiguous definitions for religious terms is responsible for a great deal of confusion and hatred. It makes dialog between Agnostics and Theists very difficult.
An agnostic usually holds the question of the existence of God open, pending the arrival of more evidence. They are willing to change their belief if some solid evidence or logical proof is found in the future. However, some have taken the position that there is no logical way in which the existence or the non-existence of a deity can be proven.
Link for definition above.
Agnosticism - The philosophical belief that knowledge of God is impossible because of the inherent, insuperable limitations of the human mind. The term was coined by T.H. Huxley about 1870, who, though not the concept's originator, was perhaps its most widely known champion in the latter half of the 19th century.