A quantum state is a mathematical description of a physical system in the realm of quantum mechanics. It encapsulates all the information about a particle, such as its position, momentum, and energy. Unlike classical states, which can be clearly defined, quantum states can exist in multiple possibilities at once, a phenomenon known as superposition. This means that a particle can be in several states simultaneously until it is measured. When a measurement occurs, the quantum state "collapses" to a single outcome, revealing a specific property of the particle. This behavior is fundamental to understanding the nature of particles like electrons and photons, and it challenges our classical intuitions about how objects behave in the universe.