One of the basic functionalities of BizTalk server is to offer Business to Business (B2B) communications between customers and business partners. The basic entities required to achieve this functionality is the Partners and their Business Profiles - referred to as Parties and Agreements in BizTalk server language.
Party (Trading Partners)
Party is the business entity with the capability of being able to send and receive messages with other parties in the server environment. For e.g., if Fabrikam wants to send a business information to their partner Contoso, there would be two parties (Fabrikam and Contoso) for the transaction. Fabrikam should create the two new trading partners (parties) to enable the message transactions between the two parties.
The profile information of the trading partner is simply referred to as the business profile. For instance, if an organization (party) has multiple divisions, each division can have its own business profile as a subset of the party information. Let's take the same scenario as before - when Fabrikam wants to send a business information to their partner Contoso, and Fabrikam has two divisions "Inventory" and "Shipping" while Contoso has one division "Purchase". In this case, since Fabrikam is responsible to send the information to Contoso, they must create the party information for both Fabrikam as well as Contoso and define the business profiles (for themselves and Contoso) within the party information.
The importance of having a business profile is to represent the different divisions in the organization clearly and define how each business profile will interact with the other party business profiles.
As the name implies, partner agreements are the agreements between the trading partners involved in a B2B communication. Agreements define the bi-directional message properties between the two business profiles of the parties. In simple terms, an agreement is the understanding between two business profiles while exchanging messages between each other. As with the previous example of Fabrikam and Contoso, lets say one agreement to be like "Fabrikam's Shipping and Contoso's Purchase business profiles should use X12 agreement standard during message transfers".