"So, what is a 'miniature infomercial'?"
Watch a really, really old show, like Burns and Allen. There's a segment in every episode where one character will awkwardly barges into a scene and start talking about the sponsor's product. The other actors react in character (as well as they can; it's rather forced) for a minute or so, then the interrupter will wander off and the main plot resumes. That's a mini-infomercial.
Modern shows do it more subtly with the characters shown driving the sponsor's vehicles with the camera centered on the brand badge or consuming a sponsor's beverage with the label carefully turned towards the camera. But soon they'll start actually mentioning the products in modern shows: "Wow what a great new car this is!" (followed by exchange on the virtues of said car) or "I just love drinking *soda/beer brand x*!" (followed by discussion of how the other character loves it too).