Ayamatma Brahma is the Mahavakya described in the ancient Hindu scriptures and Upanishads of India..
Mantra
मंत्र - Mantras are sounds, syllables, vibrations or group of words in Sanskrit language to obtain psychological and spiritual powers. Man means mind, and tra means vehicle or instrument: a tool to transport/transform the mind from one state to silence state. Mantras now exist in Hinduism, Buddhism, Jainism, and Sikhism, and sounds as per its existence.
ॐ (Om) is shortest and simplest one word mantra, also known as bija (seed) mantra. Like Om, Shanti Mantra and Gayatri Mantra are common and fundamental mantra for daily uses.