This topic applies to the Power Query Formula Language which can be used with Power Query and Power BI Desktop to build queries that mashup data. See the list of function categories.

Performs the function on each item in the list and returns the new list.

List.Transform(list as list, transform as function)  as list  

listThe List to modify.
transformThe transform to apply.
List.Transform({1, 2}, each _ + 1) equals { 2, 3 }