In the 3-2-1 backup strategy, what does the 2 stand for?

In the 3-2-1 backup strategy, what does the 2 stand for?

• 2 different admins
• 2 different locations
• 2 different media types
• 2 different copies 

EXPLANATION

The 3-2-1 backup strategy states that every bit of data should be backed up to, at the very least:

• 3 different copies
• 2 different types of media
• 1 off-site backup

This helps to ensure that if a copy is corrupt, there will be another copy available; that if there's something wrong with the primary media type, that there will be an additional media type to try; and that if something bad happens at the primary site to cause everything to be lost there, at least one other copy will be available to restore from elsewhere.
It does not include any details about how many backup administrators should be available, although having backup administrators is rarely a bad idea.
An external source that talks about this backup plan is http://www.networkcomputing.com/storage/3-2-1-backup-rule-recovery/108368175