A boundary is a real or imaginary line that separates two things. In geography, boundaries separate different regions of the Earth. There are many different types of boundaries.
A physical boundary is a naturally occurring barrier between two areas
A good example of a physical boundary could the Pyrenees Mountains that seperate Spain and France. (The mountains are 491 km (305 mi) in length)
Political Boundaries are official lines that countries, nations, states, cities, etc...
Political Boundaries are mostly influenced by physical boundaries
A good example of a political boundary could be states in the United States. States like Texas and Mississippi along with its neighboring states are influenced by physical boundaries like the Rio Grande River or the Mississippi River.
A cultural boundary is a boundary line that divides places based on ethnicity.
Chinatown in New York City is a perfect example of a cultural boundary.