Start with what the Oldsmobile Series 28 is: a car with gasoline engine, from Oldsmobile. What it meant takes a little longer.
How it came about
The Oldsmobile Series 28, also known as the Autocrat, was a mid-level four seat passenger car produced by GM's Oldsmobile Division for 1911 and 1912. It was based on the top-level Oldsmobile Limited (Series 23, 24, 27) while using a four-cylinder engine, and was manufactured in Lansing, Michigan.
The hardware
The engine is gasoline engine. These are manufacturer figures carried by Wikipedia and Wikidata, not road-test measurements.
Family and rivals
Its Oldsmobile stablemates include the Oldsmobile 442 and the Oldsmobile 88.