Place value is a mathematical concept that refers to the position or place of each digit in a number. It helps us understand how big a number is by determining its value based on the position of its digits and their values. For example, in the number 4357, the "thousands" digit has a value of 4 (since it's in the thousands place), the "hundreds" digit has a value of 3 (since it's in the hundreds place), the "tens" digit has a value of 5 (since it's in the tens place) and the "ones" digit has a value of 7 (since it's in the ones place). By understanding place values, we can better understand how to manipulate numbers, perform calculations, and compare their magnitudes.