# What is the “smearing” in heavy-ion collisions?

I often saw the word "smearing" in some papers. I don't know what it means. This word doesn't have an appropriate interpretation which is related to physics in chinese. So I feel hard to get the key point. How to expain it in physics?

More specifically, I'm doing a research about a MC event generator. The professor asked me to do the "Gaussian smearing". It seems like for the purpose of take the event fluctuation into consideration? Why are this process necessary? I'm not sure and totally puzzled. Thank you!

In physics the use means to impose an envelope, so that the clean mathematical definition of a trajectory, for example, is extended to probable points due to some physical function guessed at or derived. so instead of getting a trajectory $f(x,y,z){}$ you get a smeared trajectory, with an uncertainty around each $x,y,z$, due to the uncertainties in the measurements or original assumptions. It is a way of introducing errors in measurements.