A mid-page unit, or MPU is a square or rectangular online advertising format, usually found embedded within the content of a web page.
This format is also known as a 'Multiple Purpose Unit' because it acts as a flexible shaped blank ‘canvas’ on which an advertiser can serve flat or more interactive content as desired.
Sizes have been standardized to some extent; they are:
|MPU ad formats||width by height|
|Large rectangle||336 by 280|
|Medium rectangle||300 by 250|
|Square||250 by 250|