Deleting or physically destroying a record so it no longer exists in usable form. One outcome of disposal, and one that should be controlled and documented where required.
Destruction is the most familiar disposal outcome, but under the Act 'disposal' is broader and includes alteration and transfer of control. Deleting from an inbox may not be true destruction if copies , and destruction should be controlled and documented where required.
Not necessarily. If copies remain in other systems, deleting one instance is not full destruction. Destruction means the record no longer exists in usable form, and for records it should follow your disposal authority and be documented.
IAR turns terms like this into working practice: assets classified against your disposal authority, stewarded by position, and ready to evidence.