Mahāvākyas are big and important sentences or phrases that are often found in ancient Indian texts called the Upanishads. These sentences are really powerful because they contain fundamental truths about our existence and are believed to be revealed to great sages or enlightened beings.
For example, one mahāvākya is "Aham Brahmasmi" which means "I am Brahman". Brahman is considered the ultimate reality in Hinduism, and by saying "I am Brahman", one is acknowledging that there is no separation between oneself and the divine. Another mahāvākya is "Tat tvam asi" which means "Thou art That". This one is particularly tricky as it suggests that what we think of as our individual selves is actually the same as the ultimate reality.
Mahāvākyas are meant to help us understand our true nature and see beyond our limited perspectives. It is said that by meditating on these sentences and understanding their meaning, one can attain spiritual liberation or Moksha. So, when you hear a mahāvākya, remember that it is a really big and important sentence that contains a truth so profound that it can change the way we see ourselves and the world around us.