According to ICH-E9 guideline on statistical principles for clinical trials:
A statistical analysis plan is a document that contains a more technical and detailed elaboration of the principal features of the analysis described in the protocol, and includes detailed procedures for executing the statistical analysis of the primary and secondary variables and other data.
There is two types of plans.
- The first is a data analysis plan specific to a particular experiment - this is standard, for example, in clinical trials. See, e.g. links here http://stats.stackexchange.com/questions/118615/resources-to-write-a-statistical-analysis-plan
- The second type would be general procedures for a whole lab. This is useful to have, because then the specific plan can be much shorter, because it only need to specify deviations from your general plan for a particular experiment. See example here https://github.com/TheoreticalEcology/Green-Lab-SO
The data analysis plan goes hand in hand with pre-registration, and there is some interesting stuff going on here, see https://cos.io/prereg/ and experience here http://ecologybits.com/index.php/2016/11/16/thoughts-on-preregistering-my-research/