what is Yahweh and what is the relevance to Freemasnry?

Yahweh—frequently rendered in Masonic literature as Jehovah or the Tetragrammaton—represents the four-letter Ineffable Name of God, signifying the self-existent essence of the Creator 1. In Masonic tradition, the name symbolizes the idea of the true God and occupies a significant place in the historical development of ritual 1.

In the Craft during the early eighteenth century, the name Jehovah functioned as the Master's Word in the Third Degree and appeared inscribed on emblems and tracing boards 1. Early Masonic writers record that the name was later transferred from the Master Mason degree into the Royal Arch system 1. Within the Royal Arch, the Tetragrammaton is maintained as the True Word 1. Although ritual innovations in some English and American jurisdictions temporarily replaced it with alternative divine names, governing bodies subsequently moved to restore the Tetragrammaton to its proper place 1.

In the Scottish Rite, Albert Pike interpreted the traditional attempts to ascertain the True Name and its pronunciation as an allegory representing humanity's loss of true spiritual knowledge and the uncultivated notions of Deity held throughout history 2.

Broadly across Craft Masonry, Jehovah is recognized as one of many traditional divine names. While an individual brother may petition Deity as Jehovah, Allah, or another sacred name in private devotions, the lodge uses the overarching title of the Great Architect of the Universe to accommodate Masons of all faiths upon a shared altar 34.