Equations have the property that we have a right hand side (rhs) that is equal to a left hand side (lhs), for example
$\nabla^2(\psi)=f$
This is known as Poisson's equation. This can be re-written as
$\nabla^2(\psi)-f=0$
What is the proper English term for the $\nabla^2(\psi)-f$ part of the equation?
It's not an called an operator as an operator is something that is applied to the dependent variable $\psi$. Is there a proper term for this other than the lhs of the equation? Or, in other words, how does one call components of an equation. If it helps, how would one call the components of an equation that are equal to 0?