FIX-3-5 is a version of the Financial Information eXchange (FIX) Protocol, which is an electronic communication protocol used commonly in the financial services industry to securely exchange financial data between institutions. It is also commonly used to execute and confirm trades.
FIX-3-5 is a set of specifications and implementation guidelines for transactions and order management. It defines message formats and components, message sequencing conventions, and session-level handling rules. It also defines message types for activities related to trading, market data, membership, user authentication, and latency data.