in your passport
that allows you entry into a certain country. Usually a seal
of that nation
with some bureaucratic blabber
added for good looks. Since passports
are usually 20 to 30 pages long, you run out of space for visas
fairly quickly, especially if you travel
The need for a visa, which takes anything from 2 hours to a month to obtain, depends on what country you're flying to. Citizens never need visas for their own countries. Some countries, such as Australia, Canada and Japan, are fairly lax and don't require visas for visitors from friendly countries, such as America. Others are extremely annoying with their visa requirements, such as America and China, requiring frequent renewals and heavy fines for people who overstay.
The petty bureaucrats often try to examine your visa to find a mistake in order to pounce on you. Hence, do try to maintain a valid visa, or you risk getting sent back to where you came from. I found that out the hard way today. My visa was valid, they just can't read English! Communists. Another day in chiggerland.