What is “public domain” and how is it used?

from a legal perspective, the public domain is the space where no intellectual property rights exist. This means that works in the public domain may be used without any restrictions whatsoever. Works enter into the public domain in different ways. First, works whose copyrights have expired are in the public domain.Explanation:

professionals can use many types of technology that can them. some examples are, computers (they research and can use for programs for data, they are also used for job applications, school work, and even to make new ideas), speedometers (can get data for unknown data), sometimes something as small as a pen (used for rough drafts, to insert data, and again job applications).