Explain Like I'm 5 (ELI5)

Different words for the same or similar colors.

Starting with fully saturated orange at 50% lightness, you can decrease the lightness to zero. Along that path you will first encounter colors that could be called "light brown" or also "dark orange" (e.g., around 30% lightness). If you keep decreasing the brightness you will encounter what is typically referred to as "brown" (40%) and later on "dark brown" (15%). You could also call these later colors "dark dark orange", but nobody does.

The names of these colors are determined by convention, perception, and context. There may be multiple common names for the same color value.