Can somebody explain the 'single-core' description in the tests? Doesn't the number of cores need to be taken into account when considering the actual performan

Can somebody explain the 'single-core' description in the tests? Doesn't the number of cores need to be taken into account when considering the actual performance? This may be wrong, but the way I'm looking at it is like comparing the power of a 4 cylinder car vs an 8 cylinder but measuring the power that comes only out of one cylinder as your comparison measurement. It is possible that a single cylinder from a 4-banger creates more power than a single cylinder from an 8, but in the real world, that won't matter. I'm guessing I'm wrong, but why?