The correct answer is B. Reusable pieces of search processing language.
The explanation is as follows:
* Search macros are knowledge objects that allow you to insert chunks of SPL into other searches12.
* Search macros can be any part of a search, such as an eval statement or a search term, and do not need to be a complete command12.
* You can also specify whether the macro field takes any arguments and define validation expressions for them12.
* Search macros can help you make your SPL searches shorter and easier to understand3.
* To use a search macro in a search string, you need to put a backtick character () before and after the macro name[^1^][1]. For example, mymacro`.