Some data types are considered “primitive”, meaning they are not treated like an object and don’t have the properties of an object.
On most platforms, integers and characters are examples of types that are primitive but can be boxed.
Boxing means wrapping them in an object so they have the behavior of an object.
The exact meaning and behavior depends on the language you’re using. Some languages (such as Smalltalk… at least waaay back when I was doing it…) don’t allow any primitive types and consider everything to be an object, but there’s a performance penalty associated with that because, at the end of the day, the processor needs to work with raw numbers and raw memory to do useful work. If you want to add two integers that have been boxed, for example, behind the scenes they are “unboxed” into primitive types, the numbers are added, and they are then boxed back into a new integer.