PARAMETER_SNIFFING = { ON | OFF | PRIMARY} enables or disables parameter sniffing. This is equivalent to Trace Flag 4136.
SQL server uses a process called parameter sniffing when executing queries or stored procedures that use parameters. During compilation, the value passed into the parameter is evaluated and used to create an execution plan. That value is also stored with the execution plan in the plan cache. Future executions of the plan will re-use the plan that was compiled with that reference value.
References:https://msdn.microsoft.com/en-us/library/mt629158.aspx