What is a project baseline?

It defines a logical closure of any deliverable or cycle.
Example you have completed the requirement phase with sign off from the client on the requirement document.So you put a baseline and say that further any changes to this document are change request.
Versioning of source code is one type of baseline.

A baseline is a complete copy of a project plan that yu can compare to the current schedule to evaluate progress.
The simplest baseline plan is a complete copy , or snapshot of the original schedule.
This snap shot provides a target against which you can track a projects cost, schedule and performance.

A project Baseline is a point where the project is based from.
It usually represents the initial view of project timeframes and resources.
Once it is approved and kicks off is a typical time to baseline the project.
Any variations from baseline then, should have an explanation.
For example, there may be change requests, or a particular activity ran late.
Variations and their reasons are usually reported to the project board, and at the PIR a history of how the project varied from baseline will contribute to the learning database.

I am agree with Binil Paul Anisuddin Siddiqui and Hafiz syed only, please read and further explain my question “What are Program of Works, Clause14 Program and Baseline Program?“ in the specialty of project evaluation, project management or project planning.

A Project baseline is a snapshot of project after you complete it in all respect and got approval from authority but before you start updating it with actuals.
The baseline is then used afterwards to compare Project performance against baseline to assess the project progress and locate problem area.

Per PMI, the project’s baseline consists of
1- The scope baseline that includes project scope statement, work breakdown structure and WBS dictionary.
2- The cost baseline which is a time-phased budget used in monitoring and measuring cost performance throughout project life cycle that includes a budget contingency to accommodate for risks.
3- The schedule baseline which is an approved snapshot of the project schedule.
All three baselines represents the project's baseline that is used to measure how the project deviates from the plan in meeting the project goals.

In project management A project’s baseline is defined as the original scope, cost and schedule.
The project’s baseline must be completely defined and documented before the project execution and control activities can begin.
Time, cost and scope it the first plan of any project to success

Project baseline is a project which is a bench mark to monitor the current progress of your project.
In some programs for planning and scheduling it is also termed as target project.
Any project before being fixed as a project baseline requires approval form all stake holders of the project.

In project management, the baseline is the original range, total cost and schedule of a project. It is used to measure the amount of deviation of performance from the original plan. Before the execution of the project, the baseline must be properly defined and documented.

Baseline Plan of any Project basically the agreed copy of proposed Project Plan from the begining to Completion or End of Project.

It provides help during execution to compare the current activity schedule / Plan and defines the standing of on going Project during various stages of Project Progress.

It simply defines the Planned duration of a project , setting a planned start and end date. These baselines are based on the estimations in terms of Project scopre as well as Resource availability. The benefit it is be able to track when we are by passing the planned periods , either before starting or while in progress and moving towards the Planned delivery date