What is the collective name for the digits before and after decimal point?
The part before the decimal point, the whole number $120$ in your example, is often referred to as the Characteristic and can be seen here https://mathworld.wolfram.com/Characteristic.html. The part after the decimal point, the fractional part $590$ in your example, can be referred to as the Mantissa. More information on this can be found here https://mathworld.wolfram.com/Mantissa.html.
Hope this helps!
It's called the Number of Significant Figures. https://en.wikipedia.org/wiki/Significant_figures