A self-signed or self-signed certificate is an SSL certificate that the user has created themselves. Technically, it is no different from paid certificates, but when visiting a site with such a certificate, the visitor will see a warning:
This connection is not secure (Firefox)
This connection is not private (Safari)
Your connection is not private (Google Chrome)
Anyone, even a fraudster, can create a self-signed certificate. Therefore, the browser prompts: the site contains a certificate from an unknown manufacturer, we are not sure that it can be trusted. Even if the site is reliable, an unprepared person may be afraid of an error and close the tab.
Such situations do not happen with paid SSL certificates. They are issued by special organizations - certification centers. They check every order and take the risk that the certificate will be obtained by a fraudster. Over the years, several certificate authorities have developed a reputation for trustworthiness, so popular browsers recognize their certificates automatically.
