What is random error?

Answer 1

Random error is the name given to unforeseen mistakes that occur under secure conditions for various scientific and non-scientific procedures. For instance a mechanical instrument used weighing objects that was affected by unforeseen conditions, such as weather, and even though all necessary pre-cautions were taken, the machine may have given the observer an off the mark weight.

Perhaps the observers interpretation of the scale was improper, thus resulting in small degrees of error between that of the actual weight and that of which is observed. This is why scientist conduct their experiments dozens upon hundreds of times, taking multiple measurements and averaging them, to try to minimize random error.

Random error is the opposite of Systemic error.

The most important thing to remember to understanding what random error is, is that as the name implies it's unpredictable (random).