The user can remember and recall everything that they have ever experienced, encountered or learned in their lifetime. The user needs only to read, hear or see something once and they will never forget it. They continue to learn for the rest of their lives and their brain will simply compress neural synapses to contain it all, allowing memory of every event, experience or bit of knowledge from birth to the present. Their mind is also entirely immune to Memory Manipulation, unless the ability is first negated or stolen.
Many users who are said to only possess Enhanced Memory actually possess Panmnesia, and many who are said to possess Panmnesia only possess Enhanced Memory (the two are often confused).
Sage/Tessa (Marvel Comics) can call on her past experiences...
...to constantly improve her strategical tactics.
Tatsuya Shiba (The Irregular at Magic High School) A side effect of a procedure gave Tatsuya perfect memory, allowing him to recall all of his memories with complete accuracy ever since the day of the experiment. In his own words "It is no longer possible to forget."
Hieda no Akyu (Touhou Project) Memory of Gensokyo, The Ninth Savant, is the current "Child of Miare", who is born in the Hieda family once in every few hundred years with the ability to "not forget anything she sees" and record Gensokyo's history.
Rezkin (King's Dark Tidings)
Alakazam(Pokemon) is said to have an excellent memory and can remember everything that it has experienced since hatching as an Abra,