This message comes from syslogd(1M), the facility that prints messages on the console and records them in /var/adm/messages. To reduce the log size and minimize buffer usage, syslog collapses any identical messages it sees during a 20 second period, then prints this message with the number of repetitions.
Look above this message to see which message was repeated so often. Then consider the repeated message and take action accordingly. If repeated log entries such as su ... failed appear, consider the possibility of a security breach.