Explanation
OPTIMIZE_FOR_AD_HOC_WORKLOADS = { ON | OFF }
Enables or disables a compiled plan stub to be stored in cache when a batch is compiled for the first time. The default is OFF. Once the database scoped configuration OPTIMIZE_FOR_AD_HOC_WORKLOADS is enabled for a database, a compiled plan stub will be stored in cache when a batch is compiled for the first time.
Plan stubs have a smaller memory footprint compared to the size of the full compiled plan.
Reference:
https://docs.microsoft.com/en-us/sql/t-sql/statements/alter-database-scoped-configuration-transact-sql