How do you define squatter?

[Sam Leon]

or specifically, if an owner Alan rented a property to a tenant Bob, and the tenant sublet it to someone named Charlie.

Now Charlie lives there and the property is foreclosed.

Alan and Bob are no longer in the picture.

Charlie is not leaving, property is listed but bank can't show the property.

Listing agent said the property will probably go to auction.

Now why would the bank not evict Charlie or offer him cash for keys?

Is Charlie technically a squatter or no?