If you want to get technical, Tantra is a Hindu or Buddhist mystical or ritual text, dating from the 6th to the 13th centuries.
also, the adherence to the doctrines or principles of the tantras, involving mantras, meditation, yoga, and ritual.  

Tantric massage, however, is a style of massage that emphasizes breath, control, and sensation over orgasm. there's normally a bath/shower involved, Lingam massage is not the same as a hand-job per se, because the experience isn't about the orgasm. its about receiving pleasure to that area without feeling the need to orgasm. Now, being that we're in this line of work, orgasm is obviously worked in.  Nudity may or may not be a part of this experience. This is also one of those things that if you asked 100 different tatric massage practitioners, you'd receive 100 different answers. see also:

"Tantra massage is a type of massage that uses sexual energy to achieve a higher state of consciousness. Skilled tantra massage therapists, or lovers who study the art, use specific sensual touches such as lightly running fingertips along the entire body to awaken a dormant energy field within the body."

Nuru, on the other hand, is basically body to body massage that's done with a very slippery water and seaweed based gel that makes slipping and sliding around on each other super fun. this is a full-body massage where both you and the provider are nude (at least that's how I do it).