In Projects Management world there was a concept known as "re-baseline" . What does it mean ?

With a continuation of Mr. Alex answer. I will add the following:  

This might be done on a reactive basis just because things have changed and you realize that you are so far out of whack that you must update.

On the other hand, for long projects with a high level of uncertainty, you might agree up front that you will rebaseline at certain critical points - when key decisions are made, or when you get within a certain time of activities. It's good to have that kind of discussion with your management up front - that way you all understand the uncertainties and how you will be managing them.

After establishing a"baseline" cost estimates and schedules based on beginning assumptions. At the very beginning of a project there is a lot of uncertainty, so it's really only a ballpark estimate at that point. As things develop, you start to remove some of the uncertainty. Also, situations change - the concept for the project might change, resource availability might change, costs might go up, etc.

"Re-basline" means that the information has either matured or changed enough to warrant updating your assumptions and doing exactly what it says - issueing a new revised baseline estimate and schedule. 

Thanks for invitation...

with answer of En.ALex AL-yazouri.

answer already given and only to vote up, but a useful question, thank you

I endorse Mr. Alex's answer

A cost baseline is an approved time phased plan. Once a detailed budget is developed and approved, the project manager should publish this baseline and set it as a point of comparison for actual performance progress.

One of the biggest challenges a project manager faces is determining when to set the baseline for the budget. A baseline is an approved time phased plan. Creating a baseline should not be a 'scary' thing. It is just a starting point from what to measure performance against.

There will always be unknowns in the project, especially early on. Accept that projects will always experience changes and evolve in order to ensure delivery of the scope defined. The baseline budget is the tool for measuring how project changes affect our schedule and budget.

Ideally, new baselines should only be added when there is a change in scope. If the scope stays the same, then there is not a need to add a new baseline. Again, the baseline is a benchmark to measure performance against. It represents an understanding of the costs of the project based on the scope of the project. The initial baseline is usually what gets budgeted in a company's financials.

As you start a project, you draft an estimate of overall cost but as the project goes on, some factors change e.g cost of materials, availability in the market, efficiency of labor etc so you get back on the drawing board and set another draft in accordance with new materials and changes.

While managing a project, we establish "baseline" cost estimates and schedules with start and end dates based on beginning assumptions.as it is beginning of a project there will be lot of uncertainty.As things develop, we will modify removing some uncertainties. Also, situations change - the concept for the project might change depending on resource availability."Re-basline" means that the information has either matured or changed enough to warrant updating your assumptions.like creating a plan and track the reality based on the re baseline.

When you are managing a project, you establish "baseline" cost estimates and schedules based on beginning assumptions. The thing is, at the very beginning of a project there is a lot of uncertainty, so it's really only a ballpark estimate at that point. As things develop, you start to remove some of the uncertainty. Also, situations change - the concept for the project might change, resource availability might change, costs might go up, etc. "Re-basline" means that the information has either matured or changed enough to warrant updating your assumptions and doing exactly what it says - issueing a new revised baseline estimate and schedule. This might be done on a reactive basis just because things have changed and you realize that you are so far out of whack that you must update. On the other hand, for long projects with a high level of uncertainty, you might agree up front that you will rebaseline at certain critical points - when key decisions are made, or when you get within a certain time of activities. It's good to have that kind of discussion with your management up front - that way you all understand the uncertainties and how you will be managing them.

This is a common practice to re-do the baseline in light of significant changes or variations of the assumptions upon which the original baseline was done. You find this more in projects of unknown/unpredictable nature mostly dealing with intangible things as in the case of complex IT solutions projects possibly done for the first time and with no past experience to support the original (initial) baseline !