Can anyone explain me the meaning of this expression?

Expression:

nod.X=other.X | nod.Y=other.Y

nod is a sprite object and other is a family which only consists of nod.

nod.X=other.X | nod.Y=other.Y

I assume this is expression in a IF condition. it means:

if (nod.X=other.X or nod.Y=other.Y) It is true if one of the conditions is true.

If you want to look if a instances of the nod object have the same x or y position. You have to use a family for that. Because if you have more than one instance of nod you would compare nod with itself. You need a family to compare against something. So you put the nod also in a family.