What does uf stand for on a 10V 100uf capacitor in electronics?

The notation uf stands for microfarads or 0.000001 Farad. This is the designation of the capacitance of the capacitor. Yours is 100uF or 0.0001F

10V simply means maximum operating voltage. In short, if you exceed the voltage of 10V (volts) on the capacitor terminals, it will simply fail once and for all.
100uF - it was probably 100µF (one hundred microfrarads) means its capacitance. You will find the definition of a farad in physics books and a microfarad is one millionth of a frard. In practice, there are also millifarads (mF), nanofarads (nF) and picofarads (pF). read in any book on the basics of electronics. Good luck.