what is the definition of a Wrapper?

In the context of Trojans, what is the definition of a Wrapper?

A.
An encryption tool to protect the Trojan

B.
A tool used to bind the Trojan with a legitimate file

C.
A tool used to calculate bandwidth and CPU cycles wasted by the Trojan

D.
A tool used to encapsulate packets within a new header and footer

Explanation:
Wrapper does not change header or footer of any packets but it mix between legitimate file and
Trojan file.