Message count is the number of messages the Integration Service reads from a real-time source before it stops reading from the source. -1 indicates an infinite number of messages.
For example, if the message count in a JMS session is 100, the Integration Service stops reading from the source after it reads 100 messages. It processes the messages and ends the session.
The name of the message count terminating condition depends on the Informatica product. For example, the message count for PowerExchange for SAP NetWeaver is called Packet Count. The message count for PowerExchange Client for PowerCenter is called UOW Count.