A wave-function is a solution of the dynamical equation in the quantum-mechanical framework (non-relativistic, relativistic, perhaps even quantum field theory) of ones choice. As such, it describes the possible development (technically referred to as evolution, but having nothing to do with biological evolution) of (a pure state of) the system it describes in lieu of any further interaction. Since observation perforce includes some form of interaction (with the observer and/or her detection apparatus), the wave-function itself is of a literally limited value for predicting the future: it gives the possible outcomes of the first next observation, after which the act of observation modifies the development of the system, and the wave-function changes to incorporate that.