What is Group Policy?

Group Policy is a hierarchical infrastructure that allows a network administrator in charge of Microsoft's Active Directory to implement specific configurations for users and computers. Group Policy can also be used to define user, security and networking policies at the machine level. 

Group Policy allows administrators to define options for what users can do on a network – including what files, folders and applications they can access.  The collections of user and computer settings are referred to as Group Policy Objects (GPOs), which are administered from a central interface called the Group Policy Management Console. Group Policy can also be managed with command-line tools such as gpresult and gpupdate. In Windows Server 2008, setting extensions known as Group Policy preferences were added to provide administrators with better targeting and flexibility.

Group Policy is a hierarchical infrastructure that allows a network administrator in charge of Microsoft's Active Directory to implement specific configurations for users and computers. Group Policy can also be used to define user, security and networking policies at the machine level.

basically it's a registry settings you deploy on one or more computers that are located in a logical boundary called a Domain, these settings can have effect on the computer object or the logged in user object depending on how you configure it. 

controls the working environment of user accounts and computer accounts. Group Policy provides the centralized management and configuration of operating systems, applications, and users' settings in an Active Directory environment. A version of Group Policy called Local Group Policy ("LGPO" or "LocalGPO") also allows Group Policy Object management on standalone and non-domain computers.[1][2]

It is an infrastructure that allows you to implement specific configurations for users and computers, which are linked to the directory service containers of Active Directory.

A Group policy template of an organization describes how the company wants its workstations to adhere to the security policies including password complexity, accessing resources by users, limiting the privilages by user and computer wise policies.

a Group Policy Object (GPO) is a collection of settings that define what a system will look like and how it will behave for a defined group of users. implement on Active Directory (AD) to control , monitor , and apply global settings to all user, computers on your Domain .

for example : define user to change destop wallpaper and apply one contains you company logo 

Group Policy allows you to edit and define options for what users can do on a network (what files, folders and applications they can access). To collections users and computers settings in group to easy managment.

Group Policies are settings that can be applied to Windows computers, users or both.

Group Policies are usually used to lock down some aspect of a PC.

Whether you don't want users to run Windows Update or change their Display Settings, or you want to insure certain applications are installed on computers - all this can be done with Group Policies.Group Policies can be configured either Locally or by Domain Polices. 

Local policies can be accessed by clicking Start, Run and typing gpedit.msc.  

They can also be accessed by opening the Microsoft Management Console (Start, Run type mmc), and adding the Group Policy snap-in.  You must be an Administrator to configure/modify Group Policies.

Windows 2000 Group Policies can only be used on Windows 2000 computers or Windows XP computers.  They cannot be used on Win9x or WinNT computers.

Group Policy is an infrastructure that allows you to implement specific configurations for users and computers. Group Policy settings are contained in Group Policy objects (GPOs), which are linked to the following Active Directory directory service containers: sites, domains, or organizational units (OUs). The settings within GPOs are then evaluated by the affected targets, using the hierarchical nature of Active Directory. Consequently, Group Policy is one of the top reasons to deploy Active Directory because it allows you to manage user and computer objects.