Base 10 refers to the numbering system in common use around the world, that uses decimal numbers. Base 10 is the basis of a place value number system and is also called the decimal system or denary system.

What is base-10?

Have you used numbers 0 - 9 to count? Then without even realising, you've used base-10!
This is a way of putting a place value to numbers, its also known as the decimal system as the numerical value of a number relies on where the decimal point sits.  In base 10, each digit in a position of a number can have an integer value ranging from 0 to 9 (10 possibilities). This system uses 10 as its base number, so that is why it is called the base-10 system. Base-10 blocks are used to help children to experiment with basic addition and subtraction within the realms of base-10.

Base-10 describes how much numerical value each digit has in a whole number.
Each number = 10x (times) the value to it's right. For example:

345,862.127
Within this large number, each digit has a value of:

3 has a place value of 300,000 (three hundred thousand)
4 has a value of 40,000 (forty thousand)
5 has a value of 5,000 (five thousand)
8 has a value of 800 (eight hundred)
6 has a value of 60 (sixty)
2 has a value of 2 (two)
1 has a value of 1/10th (one-tenth)
2 has a value of 2/100th (two one-hundredths)
5 has a value of 5/1000th (five one-thousandths)