What is a Statistical Analysis Plan (SAP)?
A statistical analysis plan is a detailed document outlining the statistical analyses (both descriptive and inferential) that are planned for a given study. It is usually created prior to start of a study and for pivotal studies must be in line with regulatory requirements in terms of acceptability of endpoint analysis and with regards to prespecification.

The study protocol might get into elements of the statistical analysis plan, but the SAP goes into much more detail.