Understanding TCA Architecture in Oracle Applications: 

Oracle Trading Community Architecture (TCA) is a data model that allows us to understand and manage the complex interlinkages between the parties, customers, sites, their uses and relationships. This information is maintained in the TCA Registry, which is the single source of trading community information for Oracle E-Business Suite applications. These applications, as well as TCA itself, provide user interfaces, batch data entry functionality, and other features for you to view, create, and update Registry information.

What is the key difference between a Party and an Account? 

As explained well here in this link, the concept of a Party came into existence when Oracle bought Siebel. The main difference between a Party and a Customer is that a Party can be an entity that may/may not have bought an item/service from the company. But an account is an entity that has made a purchase in some form from the company already.

Consider a scenario where you walk into a TV store to look at the new TV models and their price. There is a fair chance that you may/may not buy a TV that fits your taste and budget and leave. In the scenario where you did not buy, but the store manager takes some basic information from you like your name, address, email id, telephone number and other details like budget and tv model. The manager then enters this information into a database where you will become a Party. This information is used by the company to send communication and marketing emails about new models and prices that may entice a Party to become a Customer. All this activity is maintained in CRM Module where the target is to make the Party a Customer and maintain relationship with the same. (In all the above scenario, you are still a Party).

Now, that you got all those emails and messages, and you got satisfied and you bought a TV from that store. Now, you became a Customer. All the transaction details related to this deal are stored using the account number. Thus, in Oracle, all the details in Accounts Receivables use the Customer account number for report generation purposes.

Can a Party exist without being a Customer?

Yes. A person may just receive information from the company but did not buy any item yet, in this scenario that person/entity is still a Party and not a Customer.

What is the use of a Party without being a Customer? 

The CRM Module main motto is marketing and it is the process of identifying, creating and retaining a Customer. The CRM looks at a Party (that is not a customer yet) as a Potential Customer and tries to reach him/her/entity with marketing emails and information. A Party becomes a Customer and more Customers bring in revenue.

Where is a Party Used? 

When a Party is created, it creates a record in HZ_PARTIES table. This is primarily used by the CRM Module.