What is an open mass system?

An open mass system is a type of system in which mass can enter or exit the system's boundaries, allowing for the transfer of matter with the surroundings. This contrasts with a closed mass system, where no mass can leave or enter, although energy transfer can still occur. Open mass systems are commonly found in various natural and engineered processes, such as biological ecosystems and chemical reactions in open containers. Understanding the dynamics of these systems is crucial for fields like thermodynamics, fluid mechanics, and environmental science.