The discussion centers on the concepts of probability density and stationary states in quantum mechanics, specifically within the context of a particle in an infinite square well. Probability density refers to the probability density function, which is crucial for determining the likelihood of finding a particle in a given position. A stationary state is defined as a quantum state that remains unchanged over time, represented by the eigenvector of the Hamiltonian. The problem requires calculating the probability density from the wave function, denoted as |ψ(x,t)|². For clarity, consulting a textbook or online resources for definitions and explanations of these terms is recommended.