What is the definition of commenalism?

I guess is

It compares with mutualism, in which both organisms benefit, amensalism, where one is harmed while the other is unaffected, and parasitism, where one benefits while the other is harmed.

In ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other.

It's basically when one thing gets a benefit without harming/effecting the other thing!