A2A refers to Ask to Answer. In various Online forums and question and answers sites like Quora, questions are asked by some user to know the answer or to give more detailed information about a topic. so the knowledgeable person in that field will answer the question. so here the term A2A comes, one user asked the question and other users will answer the topic/question.
When talking about application or systems in an Organization level or Network level
A2A refers to - Application 2 Application and
B2B refers to - Business 2 Business
