This is in response to this blog post and it’s comments (read it first).
I prefer the usage of the term Party because I also believe it is a more common abstract term. I will say this though: Customer is not a Party. It is a 'Role' that a 'Party' plays. For instance, I would use 'Person' and 'Company' as parties, and 'Customer' and 'Supplier' as roles.
This is not my own idea. Martin Fowler does a good job of talking about Accountability patterns, which is where he references the concept of a 'Party', but that concept goes much further than the Accountability patterns.
There is a much greater pattern. In fact there are two patterns - Archetype Patterns. The first is the 'Party' Archetype Pattern, and then there is the 'Party Relationship' Archetype Pattern. Both are closely related, as the latter builds on the former. These two Archetype Patterns are well covered in a wonderful, if not horribly named book: Enterprise Patterns and MDA (hereafter EPM). Many Archetype Patterns are discussed: Party, Party Relationship, Customer (which more accurately models this as a Party Role), Product, Inventory, Order, Quantity, Money, and Rule.
I would strongly recommend someone looking at Martin Fowler's Analysis Patterns for modeling ideas/concepts to also read EPM. In my opinion EPM is, in some ways, a superset of what Analysis Patterns talks about, and EPM's patterns are more generally applicable – hence usage of the term Archetype.
One final comment - with all of these patterns there are two principles that need to be applied, as Martin Fowler pointed out (Analysis Patterns, page 13):
Principle: Patterns are a starting point, not a destination.
Principle: Models are not right or wrong, they are more or less useful.