Long-term memory was the ability to form, retain, and recall internal representations of past experience.
In 2368, when asked by Worf about what she had found, Doctor Beverly Crusher noted nothing much and said, "The brain scans I've run are unusual, but there's no damage to the hippocampus. That suggests that we still have our long-term memories but somehow they're being blocked." (TNG: "Conundrum")