A sign-value system with a base of ten - the first decimal system in history. Different symbols represented powers of 10, which were then multiplied by the number of these symbols and added.
As visible on the image on the right, "1" was represented by a single stroke. Between 1 and 9 the system was somewhat unary.
A significant source of our knowledge on the Egyptian mathematics is the Rhind papyrus, which served as kind of a maths textbook.
Cover image source: https://commons.wikimedia.org/wiki/File:Edfu_Egyptian_numerals.JPG