Baseline Schedule

A baseline schedule is the timeline that you start with at the beginning of your project. When you talk about being "on time", this is what you are comparing your actual performance to. Sometimes when there is a significant change in scope, the project can be "re-baselined" - which isn't a word, but project managers use it to mena that a new baseline schedule is established. The idea being that because there is more to be done, the old baseline is not a good point of comparison to measure against.