Story points, sometimes called estimate points, are the result of the planning poker.
You may remember the Fibonacci numbers from the Planning Poker. The sequence starts from zero – 0, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89. A more common variant is 0, ½, 1, 2, 3, 5, 8, 13, 20, 40, 100. At Grooming, each task is assigned a number that the team had agreed on. These is the input for Sprint planning and sometimes, the Project Owner may look at the story points to better organize priorities. But what do they mean?
You may tend to think about the story points as slots of time. After all, a task that takes longer than a day should be split up. But this is wrong. Why? The goal of having story points is to improve sprint velocity. While the goal is to figure out new approaches (or remove impediments) to increase the sprint velocity, the time of the sprint will remain constant. Unless you add more people or increase the number of working hours for the team.
Also, more people may work on the same task to finish it, however the difficulty of the task remains unchanged. When doing time estimation (days) or effort estimation (man-days), look instead at the whole team and sprint velocity to give a proper assessment.
If the task is difficult, I.e. the story point number is relatively high, it’s a good sign that the task is too complex and should be split into smaller ones.