what is the third party how do you disable it?

Third party is someone (preferably a company) that is not in relations to or with the manufacturer of a product (Canonical) or user, but is available for use on the platform. All in all, third parties aren't related to Companies, they just publicize software on their own and worry about themselves. They aren't involved with the companies they publish to, they are independent. You can disable third party software by going to the settings through the Update manager and unchecking "Canonical and partners" it should be available in the "other software" tab.