This is an innocuous error that will occur and be dumped into the alert log of whichever SID is currently set. What it means is that someone typed “oracle” at the unix prompt. Since there is an oracle executable in the path ($ORACLE_HOME/bin) it attempts to execute, is caught by the running database and turned into an error:
Errors in file /oracle/product/admin/comm/log/ora_10718_comm.trc: ORA-00600: internal error code, arguments: [12235], [], [], [], [], [], [], []
I think the error (warning, really) could be a bit more descriptive.
So, if you want to scare the pants off the new junior DBA on their first time on call, just type in “oracle” a bunch of times, and wait for their pager to ring!