Heisenberg's Uncertainty Principle is one of the most fundamental principles in quantum mechanics. It states that there is a fundamental limit to our ability to know certain pairs of physical properties of a particle with complete precision. The more precisely we try to measure the position of a particle, the less precisely we can know its momentum, and vice versa.

This principle challenges the classical notion that we can know both the position and momentum of a particle simultaneously with absolute certainty. Instead, it introduces a fundamental uncertainty in our ability to measure these properties accurately. The uncertainty in one property comes at the expense of increased uncertainty in the other property.

For example, consider an electron. If we try to measure its position very precisely, its momentum becomes highly uncertain. Conversely, if we try to measure its momentum very precisely, its position becomes highly uncertain. This inherent uncertainty is a fundamental feature of the quantum world.