What is pr in seo fild?

Are you talking about Press Release or Page Rank? If Press Release, it is link building method that helps to build a good reputation and credibility, Also, it helps to rank up your website in SEO Bests.
If Page Rank, that was remove long time by Google to prevent the obsession of the SEO specialist to PR Juice. When Page Rank change into Authority Score. Authority Score based from quality backlinks, domains and traffic data.