please tell me what is high authority domain and its effect on SEO?

A domain with high reputation, High alexa, and high PR (PR is not relevant now) can be treated as high authority domain.

Ex : Wikipedia

A link from high authority domain is valuable than 100s of links from low quality directory or bookmarking sites.

A high authority domain will increase your rank for a prolonged time and will provide the same authority to your site. This will increase the trust flow of the search engines towards your domain.

Well, in order to understand high authority domain you need to know what is Domain Authority. So what is Domain authority - You can say it as a measure of the power of a domain name. It's based on three factors i.e Age, Popularity, and Size.So I guess this three factors itself clears that the site having higher domain authority means more will he chances that it can rank over the SERPS and getting a link from that domain mean you also have the higher chances of seeing yourself over the SEPRs.