A visa generally gives non-citizens permission to appear at a foreign port of entry to apply for admission to a foreign country and to remain there within specified constraints, such as a time frame for entry, a limit on the time spent in the country, and a prohibition against employment. Many countries do not require a visa in some situations; this may be the result of treaties specifying reciprocal arrangements. The possession of a visa is not in itself a guarantee of entry into the country that issued it, and a visa can be revoked at any time.
A visa application in advance of arrival gives the country a chance to consider the applicant’s circumstances, such as financial security, reason for travelling, and details of previous visits to the country. A visitor may also be required to undergo and pass security or health checks upon arrival at the port of entry.