Know how to use "fewer" and "less"? Find out.
1550s, from Middle French émulation (13c.) and directly from Latin aemulationem (nominative aemulatio), from past participle stem of aemulari "to rival, strive to excel," from aemulus "striving, rivaling" (also as a noun, "a rival," fem. aemula), from Proto-Italic *aimo-, from PIE *aim-olo, from root *aim- "copy" (see imitation).
When one system performs in exactly the same way as another, though perhaps not at the same speed. A typical example would be emulation of one computer by (a program running on) another. You might use an emulation as a replacement for a system whereas you would use a simulation if you just wanted to analyse it and make predictions about it.