Agnosticism is a philosophical position stating that there can be no proof either way that God exists or doesn't exist. Agnostics believe that there may be a god, but that he/she is ultimately unknowable.
Agnosticism has two general meanings.
One is that knowledge of the divine is impossible. This definition is not to be mistaken with an alternative to atheism. Atheism and theism deal with belief, agnosticism and gnosticism deal with the basis for such belief. For example, agnostic atheism holds that knowledge of the divine is impossible(or currently unobtained) and thus belief in God is unjustified and illogical. On the other hand, agnostic theism is also perfectly valid. Any theist who says ‘just have faith’ is holding such a position, as they are admitting that they have no knowledge of whether a god or gods exist, and yet still believe despite of that. Gnostic atheism and theism are pretty much self-explanatory given that the definition of Gnostic to be ‘believing that knowledge of the existence or nonexistence of the divine is possible or currently held’. A gnostic atheist claims that he knows that god does not exist(or thinks one day such knowledge will be obtained), and thus believes that there is no god. A gnostic theist, on the other hand, believes in god because he claims to know the existence of god.
On the other hand, Agnosticism can be also used in a general sense: not believing in something without evidence. For example, agnosticism about the existence of invisible immaterial pink leprechauns inside computers, making it work. There is no evidence that they do not exist, yet assuming they do exist is almost delusional. As there is no evidence for them, the logical answer is that they don’t exist. The amount of things towards which we are agnostic about is infinite, including the infinite possibilities of extraneous things yes unthought of. Yet believing in such things is not illogical. Thus too, is belief in a god bounded. Unless strict and clear evidence is provided, non-belief is not illogical, in fact, it is the default logical choice.
Often, people claim that they are ‘Agnostic’. This is a misnomer, caused by a misunderstanding of Agnosticism, causing its use as a softened version of atheism, rather than its true meaning. What such people mean to claim, is that they are weak atheists, or negative atheists, who lack belief in god. Such a description applies to babies, and so on, people who have never heard of the idea of a god. Some would argue that agnostic better applies to people who simply don’t know what they believe yet than atheism. However, not knowing implies a lack of conviction. A belief is a conviction in something’s truth. If that conviction in the existence of god is lacking, at least implicit atheism describes such beliefs. Furthermore, that claim of simply lacking a belief in a god does not take somewhat of a middle ground. The fact that they lack belief in all gods they know of, means that they have rejected all the gods possible, which is a position of strong atheism, or disbelief, at least of all gods they know of. Therefore, all people who have no specific belief in god are strong atheists, at least towards the deities they know of. Thus, the only people who are complete weak atheists are babies, or people with no knowledge of any supposed deities.
The problem with this misunderstanding of Agnosticism is mainly due to this common scenario. Somebody asks ‘do you believe in god?’ and receives the answer ‘I’m agnostic’, meant ‘I don’t know’. However, the original question was not about knowledge, but about belief. However, as to the question ‘is there a god?’ I can logically remain agnostic, as this question deals with knowledge. To the infinitely many possible gods, however, implicit atheism is the only option, as strong atheism requires a specific disbelief in the possible deity, which in return requires specific characteristics for the deity be explained. In reference to a specific god, the position of strong atheism is perfectly valid, and possibly even gnostic atheism.
Also see: Atheist vs. agnostic