Final answer:
In the M language, also known as Power Query Formula Language, there is no type called Dataframe. The valid types are List, Function, and Record. A Dataframe is a concept in R or Python's pandas library.
Step-by-step explanation:
The student has asked which of the following is not a valid type when programming in the M language: 1) List 2) Dataframe 3) Function 4) Record. In the M language, also known as Power Query Formula Language, there is no type called Dataframe. The valid types in M are List, Function, and Record. A Dataframe is typically associated with languages like R or Python's pandas library, but is not a construct of the M language used in Power Query within Microsoft Excel and other Microsoft products.