This value defines the session garbage collector Time to Live (TTL) for your session database, in seconds.
You can navigate to Memberium -> Settings – Performance screen to set duration for Session Inactivity Timeout feature.
This setting specifies the number of seconds after which your sessions records will be seen as ‘garbage’ and potentially deleted.
The default value is 0, which uses a period of 2 weeks, to match the default WordPress cookie lifetime.
Setting it shorter can be useful to reap abandoned sessions and control the growth of your session database.