A typical inline-four engine has four cylinders.
An inline-four, also called a straight-four, places four cylinders in a single row along one crankshaft. Each cylinder contains a piston that moves up and down, and the crankshaft converts that motion into rotation to drive the vehicle. The layout is compact, comparatively simple, and naturally well suited to mass-produced cars.
Inline-fours became especially common as automakers sought lighter, smaller engines with better fuel economy. Ford’s Model T used an inline-four, and the configuration remains widespread in modern cars, motorcycles, and other machinery. Turbocharging has made it possible for many current four-cylinder engines to produce power once associated with larger engines.
“Inline-four” does not mean every four-cylinder engine has the same layout. Flat-four and V4 engines also have four cylinders, but their cylinders are arranged differently. In ordinary automotive conversation, however, “four-cylinder engine” often means an inline-four because it is the dominant arrangement.