In AWR report, there is a field in Instance efficiency % called Parse CPU to Parse Elapsd% which in most of the cases lead us to scepticism and skip this metric
To directly come to the point, this metric is related to calculation of efficiency of parsing of the SQL statements with CPU
The amount of CPU time by SQL that is spent on parsing or waiting on an event to parse (ie)
For every second of CPU , the amount of clock time spent in parsing or waiting by database
Higher the ratio better the instance efficiency which means CPU time = Parse time ==>(Efficiency = 100%) and CPU is effectively used for parsing itself which is its purpose
Lower the ratio, which means there is a parsing issue (application not reuse the SQL) in the database or SQL is waiting on some events latch or mutex to parse which is not good.
Example: As the ratio in itself says, ( parse time cpu / parse time elapsed ) * 100
( 12527/401081 ) * 100 = ~3.12