It can be used in a few different ways:
* Decimo (abbreviation: Dec.) can be used as a prefix to indicate something is tenth in a series, similar to how we might use "Volume 10".
* Decimo (abbreviated Dec.) is also commonly used as a way to refer to the tenth grade in a school system.
* Decimo can also be used to refer to a tenth part of something, similar to how we might refer to a tenth of a liter.
Here are some examples:
* Decimo anno - In the tenth year
* Decimo libro - The tenth book
* Decimo grado - Tenth grade
* Decimo parte - Tenth part
It's important to note that "decimo" can sometimes be used in a more general sense, meaning "tenth" or "ten", but it is most commonly used in the context of something being tenth in a series or a tenth part of something.