Sentence:  In Perl, variable <WSD>interpolation</WSD> happens in double-quoted strings and patterns, and list <WSD>interpolation</WSD> occurs when constructing the list of values to pass to a list operator or other such construct that takes a <code>"LIST"</code>. 
Meaning of the word marked with <WSD> tags:  During the course of processing some data, and in response to a directive in that data, to fetch data from a different source and process it in-line along with the original data.