ssl/server_cache_size is a SAP Parameter attribute which is used to control Size of the server side SSL session cache information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
With this parameter, you can specify the maximum size of the cache for SSL server sessions. If an SSL server session can be negotiated successfully sith the client, it is stored in the cache with the result that further accesses with the same client can take place with a shorter and more effecient authentication (provided the client controls the SSL session caching on the client side).
The duration for which a session can be reused in the cache is restricted. At regular intervals (1/4 of the session lifetime) sessions are deleted from the cache that have exceded their life. When the cache's upper limit is reached the system first tries to delete all sessions that have exceded their life. A displacement according to LRU strategy (last recently uses) is applied so tha a new session can be accommodated in the cache.
The life of a server session can be changed with profile parameter "ssl/server_cache_lifetime".
See SAP Parameter Documentation for full SAP documentation for this profile parameter.