So I'm not sure what type of border you are asking about or the context but I found this info and I hope it's helpful! :) Would appreciate brainliest ;)...
"A border is a real or artificial line that separates geographic areas. Borders are political boundaries. They separate countries, states, provinces, counties, cities, and towns. A border outlines the area that a particular governing body controls. The government of a region can only create and enforce laws within its borders.
Borders change over time. Sometimes the people in one region take over another area through violence. Other times, land is traded or sold peacefully. Many times, land is parceled out after a war through international agreements.
Sometimes, borders fall along natural boundaries like rivers or mountain ranges. For example, the boundary between France and Spain follows the crest of the Pyrenees mountains. For part of its length, the boundary between the United States and Mexico follows a river called the Rio Grande. The borders of four countries divide Africa’s Lake Chad: Niger, Chad, Cameroon, and Nigeria.
Borders—particularly national borders—affect travel and migration. People can usually move freely within their own country’s borders, but may not be allowed to cross into a neighboring country.
When neighboring countries have similar wealth and political systems, their borders may be open and undefended. For example, citizens of the 27-country European Union may travel freely among any of the member states. Only five EU members—Bulgaria, Cyprus, Ireland, Romania, and the United Kingdom—require travelers from other EU states to present a passport or ID card at the border.
On the opposite extreme, the Korean Demilitarized Zone—the border between communist North Korea and democratic South Korea—is the most heavily militarized border in the world. The zone, which is 4 kilometers (2.5 miles) wide and 243 kilometers (151 miles) long, separates the two countries with barbed-wire fences, land mines, and armed guards. Citizens of most countries must have a passport and official permission to enter the borders of North Korea. North Koreans must also have official permission before they leave the secretive nation.
Every country has its own rules about who may travel, work, and reside within its borders. Visas and work permits are government documents issued to non-citizens that limit the type of work or travel they may do in the country, and for how long. The United States issues “green cards”—officially known as permanent resident cards—that allow non-Americans to live and work inside the borders of the U.S. and be protected by its laws.
Border Protection-
Most countries have some sort of military or law-enforcement presence along their borders. Countries protect their borders for several reasons. One is to keep out invaders. This is especially true in areas where two or more countries have fought over the same land for many years. Cambodia and Thailand, for example, have disputed the territory of the Preah Vihear Temple for more than a century. Cambodian and Thai military units are positioned along the border near Preah Vihear Temple, and skirmishes often result in deaths on both sides.
Sometimes, borders serve to keep citizens in. Most governments with these “closed borders” are not democratic. In addition to North Korea, nations such as Myanmar and Cuba rarely allow their residents to cross their borders.
Borders can also serve to protect resources. Sometimes, the borders of U.S. congressional districts protect ethnic, religious, or economic communities. Citizens within these borders often vote as a unit, based on shared political beliefs. The area’s representative in the U.S. House of Representatives must be aware of the interests within his or her district’s borders. The concerns of a representative from the urban area of St. Louis, Missouri, for instance, are less likely to be issues affecting farmers than a representative from rural Missouri, which is dominated by agriculture. The representative from rural Missouri would be less likely to be concerned with issues surrounding public transportation, which is much more common in cities."
