Oracle traces 2 types of events - database calls (eg EXEC, PARSE, FETCH etc) and OS calls made.
Database call entry - name of the calll, cursor handle id, c = cpu time in usec, e =2.718 elapsed time, p = bin of oracle block, cr + consistent mode call made, cu = current mode call made, ms = no of misses from the lib cache, r = no row returned, dep = depth of the call (is the call a child of another call), og = optimised goal number (all, first, rule, choose), plh = plan hash value, tim = timestamp of the entry ( made at end of the call).
System call always identified by the word WAIT and follow by the cursor handle id, nam = descriptive name of the syscall, ela = elapsed time of the call, file #, block #, blocks = number of blocks returned, obj # = oracle object number, tim = timestamp when this entry is logged (when the call conpleted.