According to the interpretation of quantum mechanics known as the Copenhagen interpretation, when a measurement is made on a quantum system, such as a particle, the wave function describing the system undergoes a collapse or reduction. This collapse is often referred to as the wave function collapse.
The collapse of the wave function means that after the measurement, the system is no longer in a superposition of multiple states but instead "collapses" into one of the possible eigenstates corresponding to the measured value. This collapse is a fundamental aspect of the Copenhagen interpretation and is responsible for the probabilistic nature of quantum measurements.
Heisenberg's uncertainty principle states that there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be simultaneously known. When you perform a measurement to determine the momentum or position of a particle more accurately, you are effectively reducing the uncertainty in one property at the expense of increasing the uncertainty in the conjugate property.
In the context of the wave function collapse, making a measurement to determine the momentum or position of a particle more precisely would involve a corresponding collapse of the wave function. The wave function would "collapse" into a state that provides information about the measured property with greater certainty, while introducing greater uncertainty in the other property.
It's worth noting that there are alternative interpretations of quantum mechanics that propose different ways to handle the measurement process and the collapse of the wave function. Some interpretations, such as the many-worlds interpretation or the consistent histories interpretation, avoid the concept of wave function collapse altogether. However, the Copenhagen interpretation remains one of the most widely taught and used interpretations of quantum mechanics.