A poll is when you find out and count people's views, opinions or preferences, either by voting (a ballot) or other means, such as questionnaires or surveys.
We also have certain expressions, such as 'go to the polls' and 'a polling station' .
An election is when people vote for which candidate or candidates they want to be elected to a particular position eg a presidential election.
For example, this week there will be a referendum in Scotland in which people will vote for whether they wish to remain in the United Kingdom. This will involve a ballot, but it is not an election.