A Baseline is a minimum or starting point used for comparisons. It is a fixed point of reference that is used for comparison purposes. In business, the success of a project or product is often measured against a baseline number for costs, sales, or any number of other variables. 
Usually, a Baseline is used to evaluate the effects of a change, track the progress of an improvement project, or measure the difference between two periods of time. For example, a company that wants to measure the success of a marketing campaign can use the current sales as a Baseline against which post-campaign sales are measured to evaluate the success or failure of the campaign.