Yeh Stephen….he is right
Sibling means children of same parent.
I mean
Root1
Parent1(Record)-Child1(Field Element)
Child2(Field Element)
Parent2(Record)-Child3(Field Element)
Child4(Field Element)
Now here Child1 and Child2 are sibllings and Child3 and Child4 are siblings.
Child1 and Child4 are not siblings as they are not children of same parents.
Hope you find it useful.