Not stupid its a good question...
It means that the Bore of the cyl is larger than the length of the stroke. most often over square engines can spins faster due to the short stroke and will make high hp but lacks some in the torque dept..
From wiki so take it with a grain of salt..
Oversquare, or short-stroke engine
An engine is described as oversquare
if its cylinders have a greater bore diameter than its stroke length - giving a ratio value of greater than 1:1.
For example an engine which has 100 millimetres
) bore, and 80 millimetres (3.15 in) stroke has a bore/stroke value of:
100 mm / 80 mm = 1.25:1This is generally considered to be a positive trait, since (all things equal), a shorter stroke results in less friction on the cylinder wall, and less stress on the crankshaft
] An oversquare engine is generally more reliable,[citation needed
] wears less,[citation needed
] and can be run at a higher speed. In oversquare engines, low-speed torque
tends to be lower, since torque is relative to crank throw - the distance from the crankshaft main bearing
centre to the crankpin
(big end) centre, as well as the lowering pressure of the combustion gases as the piston descends.
Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end power, at the expense of low-end torque.
Oversquare engines tend to be lighter[citation needed
] and shorter[citation needed
] than undersquare engines of similar engine displacement
along the direction of piston travel, but they are wider in directions perpendicular to piston travel. As the length is not a large problem, these engine types are highly favored by many manufacturers because of their power and compact size.
Some Formula One
engines have a bore to stroke ratio of approximately 2.5:1, and are capable of revving to 19,000 rpm.