To answer that question it just means that one engine needs a higher revolution per minute to make the same horsepower.Basically if you are going down the road at say 70 miles per hour and your engine is turning 2000 RPM on the tach it means in one minutes time your engines crank will be turning around 2000 times.
Usually, that would be the case. A 4 cylinder tends to rev pretty high to generate HP, and doesn't have a lot of torque. A lot of power at low speeds is best for a driver. If you have plans to race at real high rpm's, you don't care so much about the lower engine speeds.
Another value that is important is torque. A longer stroke engine tends to have more torque at low speeds, commonly referred to as "low end torque". My diesel pickup has about 150 HP, but stump pulling torque. The result is a truck that outruns many cars, with less weight and lots more HP, through it's optimum rpm range.
Here is a site that will explain how torque and RPM are related. If you really want to get into the math of it all with a better explanation, THIS site will be interesting to you. Who said that high school math would never be used again?