1. MEST, or the MEST universe, refers to the universe where we find the things that make up the real world: trees, rocks, suns, mountains, atoms, chemical elements, trains, tables, chairs, etc. Spiritual beings (thetans) are not part of the physical universe, but they affect it. Beings established the agreements of this universe. Those agreements form the universal frameworks we use to communicate and interact with each other and the things around us. L. Ron Hubbard coined the word by combining the first letters of matter, energy, space and time. (Science of Survival, Chapter One, Column A | The Tone Scale)
2. MEST can also be used to refer to objects in the physical universe rather than the entire physical universe. For example, when talking about your personal belongings you could say, “I like to keep my MEST in good shape.” Items you own, like your car, clothing, home, plates, bookshelves, books, etc would be your MEST. Items owned by another would be their MEST.