Horizontal prototyping,

“ provides a wide range of functions but with little detail.”

Preece, etc.

“the functions are not implemented in detail as required in the final system, thus, they can be used for demonstration, part of their effect being omitted or simulated”

Floyd, (1984) A systematic look at prototyping, in Approaches to Prototyping by Budde, et al.

“The purpose of a horizontal prototype is to develop an entire layer of the design at the same time. ... useful to get an overall picture
of the system from the user's perspective and address issues such as consistency , coverage , and redundancy.”

Michel Beaudouin-Lafon and Wendy Mackay (2003). Prototyping Tools And Techniques