A patent definition like any legal definition, is defined by a government.
The governments of most countries have the same definitions.
Governments can change a patent definition over time. They may decide to make necessary changes because of court decisions made in litigation cases, or because of an economic advantage or change in foreign policy.
For example, the governments of some countries may allow patents for cloning animals or for genetic modifications to foods, whereas other governments may not recognize such processes as patentable.
A misconception that most people have is that a patent gives you a monopoly on your invention or that it prevents others from stealing your idea.
This isn't true.
What is true is that a patent is recognition from a government that your invention is new, unique and useful according to the patent office of that country.
That is the patent definition for a new invention.
It is true that you can attempt to stop anyone from infringing on your patent. This is done through patent lawyers who can take various actions on your behalf against the infringing parties.
This can be expensive depending on the circumstances.
Having a patent on a product doesn't mean that someone will not sue you for infringing on their patent. There are patent lawyers that specialize in this practice.
Having a patent doesn't mean that people won't attempt to make or sell your invention even though you have a patent.
One good thing about a patent is that it reduces the probability that you are infringing on someones invention.
It also allows you to communicate without the need for a non-disclosure agreement.
Companies also like to have patent because it discourages their competitors from selling the same product because they might get sued.
A patent gives a company "suing rights" which they like to have because the sole motivating factor of all successful inventions - is profit.
Less competition means more potential profit.
Who prepares and files your patent is important. This is why you do not prepare your own patent or at least have your application reviewed by a patent attorney.
Lets say you are a carpenter and you go to a job site with a plastic hammer on your belt that says "Mickey Mouse". People might think you are joking.
Now lets say, you walk into a business meeting with a patent that you did yourself. Same reaction.
It's not that your patent is not good or even poorly done. It's the perception.
In legal matters, which is what patents and patent law is all about, it's not wise to prepare a litigation document (patent) if you're not an attorney.