Manual:$wgParserCacheType

Details
Parser cache setting.

Here are the available CACHE constants, as defined in Defines.php Determined by the function ObjectCache::newAccelerator.
 * CACHE_ANYTHING - Use anything, as long as it works
 * CACHE_NONE - Do not cache
 * CACHE_DB - Store cache objects in the DB
 * CACHE_MEMCACHED - memcached, must specify servers in 1>Manual:$wgMemCachedServers|$wgMemCachedServers
 * CACHE_ACCEL - APC, XCache or WinCache, whichever is available, in this order.

Use PHP's DBA extension to store in a DBM-style database
 * CACHE_DBA -

Note
For a very large wiki (tens of thousands of pages) value of CACHE_DB might be preferable to CACHE_MEMCACHED. Although memcached is faster, it won't be able to cache everything (no reasonable amount of memory would be enough), while DB will be. Therefore DB will have much higher percentage of cache hits.

If you set $wgMainCacheType then the values for $wgParserCacheType and $wgMessageCacheType will inherit it. You do not need to set those variables unless you plan on doing something very advanced.