What is the name of the security concept that explains why Linux asks for root password?

Whenever I'm installing new software or making changes to the system, Linux asks for the root password.

What is the name of this security concept and where can I research more information about it?

Your question is a bit vague, but you seem to be asking about the principle of least privilege, which basically says that a system is most secure when each piece only has the permissions necessary to do its own tasks. This limits the possibility of damage from mistakes or malicious actions.

An ordinary user typically does not need to be modifying system-level software or configuration, and so a regular user account doesn't have the permissions to do so. For the relatively infrequent times when you do want to make system-level changes, the sudo system (or equivalent such as Polkit) provides a way for you to gain those permissions temporarily, make the changes you want, and discard them.

The technical concept you're looking for is known as Privilege Separation. With this concept, each program uses the privileges granted to the user running the application, which is enforced by the operating system's security modules. When a user needs to do something that's outside of their normal privileges, the system challenges the user in order to grant additional privileges. The intent of all this is that a rogue program (virus, trojan, etc) should not be able to do any considerable harm to a normal user account unless the user gives it additional privilege to do so. While this link is, of course, to Wikipedia, it includes links to additional articles and external resources where you can learn more about privilege separation and how it mitigates privilege escalation (taking advantage of a software bug to gain privileges/penetrate the system/etc).