Good explanation about what is EAV and how it is implemented in magento can be read here.
Magento EAV cache is expected to cache product, category, other types of EAV attributes to cache.
Since Magento CE 1.4 release EAV cache in Magento is broken. It means that descriptions of EAV attributes (product, category, etc.) are loaded from eav_attribute and other related tables on each page request for each new model/collection type creation.