Nam Myōhō Renge Kyō (南無妙法蓮華経, also transliterated Namu Myōhō Renge Kyō) is a mantra, which is recited as part of the practice of Nichiren Buddhism. This practice is referred to as daimoku (題目).
The phrase is somewhat difficult to render into English, because each word or set of words contains a complex set of symbolism and connotation. One translation, used by Nichiren Shu, is "Adoration to the Scripture of the Lotus of the Perfect Truth", but without an understanding of the symbology behind those words, the full meaning is lost. "The Scripture of the Lotus of the Perfect Truth" is a text more commonly referred to in English simply as the Lotus Sutra.
On one level, the words Myōhō Renge Kyō are the Sino-Japanese title of the Lotus Sutra, which is held by some Buddhists to be Shakyamuni Buddha's penultimate teaching. On a different level, according to Nichiren Daishonin, the mantra can be seen as a distillation of the entire sutra, i.e., all the sutra's teachings are summarized in the title. Third, it is held by followers of Nichiren Buddhism to be the Ultimate Law permeating the universe.