An opinion poll is a survey carried out to find out public opinion on a given subject. Opinion polls do not always predict the outcome of elections correctly. Some media organisations try to call the result of an election before the official results are released in all electoral districts using opinion polls together with those results that have been released.
Sometimes opinion polls are wrong because voters want to say that they support a political party whch is in the interests of the less fortunate in society where as they may vote in line with their own personal interests. Opinion polls can also be inaccurate due to flaws in sampling for example choosing names at random from a phonebook excludes those who do not have a phone or who are ex-directory. The phrasing of the question is also a very important factor.
An exit poll is a poll carried out as people leave the polling station.