Master Detail relationship is
the Parent child relationship. In which Master represents Parent and
detail represents Child. If Parent is deleted then Child also gets
deleted. Rollup summary fields can only be created on Master records which will calculate the SUM, AVG, MIN of the Child records.
Up to 2 allowed to object.
Parent field on child is required.
Access to parent determines access to children.
Deleting parent automatically deletes child.
A child of one master detail relationship cannot be the parent of another.