Neidan is a permanent concept deeply rooted in Chinese Taoist philosophy referring to "internal alchemy," which is the cultivation of inner energy. However, there are several synonyms for this term that convey a more specific meaning, such as "inner elixir," "inner refinement," "inner transformation," "inner cultivation," "inner immersion," "inner practice," "internal meditation," and "inner alchemization." Each of these words carries various nuances that make them useful in different contexts, such as meditation, traditional Chinese medicine, energy healing practices, and martial arts. Regardless of the specific context, though, all these terms refer to the central idea of harmonizing and balancing one's internal energy to enhance vitality and longevity.