What is a bija (seed) mantra?

A bija — literally 'seed' — is a single-syllable mantra that carries an entire tradition's meaning in one sound. Om is the most universal bija. Gam is the seed of Ganesha. Shreem is the seed of Lakshmi. Aim is the seed of Saraswati. In tantric practice, bijas are considered the concentrated vibrational essence of what they invoke. To chant 'gam' is not merely to name Ganesha but to invite his quality into the body through sound. Bijas are often woven into longer mantras — 'Om Gam Ganapataye Namaha' places the bija at the center of a fuller invocation. They can also be chanted on their own, especially in meditative practice.