"EvaluateInitialization" is a front end token that evaluates all the initialization cells in the current notebook.
This token is equivalent to the menu command Kernel Evaluation Evaluate Notebook.
All cells with the options EvaluatableTrue and InitializationCellTrue will be evaluated. Normally, notebooks are set up so that these cells contain definitions needed to use other material in the notebook.
To execute a front end token, you typically evaluate a command of the form FrontEndExecute[FrontEndToken[token]].