LAM is a Bija mantra. In yoga, the Bija mantras are said to be the vibrational building blocks of the universe. They don’t have any direct meaning; they are syllables that form the foundation of everything. You can find our more about them in the book Mantra and Primal Sound by David Frawley.
The mesh ka mantra was channeled by a former member of this forum from the spirit Meton.