Percent is really two words in one: per cent. A cent is a hundredth (compare: centi) so per cent means in every hundred.
You will no doubt have been given back work or exams with a mark written as a percentage. What does it actually mean?
100% = all correct
This means that tests that might have a different number of marks can be correctly compared.
e.g. 42/60 and 45/80. The last mark is higher, but its percentage is lower!