This is how I have understood this. Please correct me if I’m wrong.
Pas akum is bread baked by a private goy in his own house. This is assur according to everyone.
The bread that the OU gives hechsherim to is pas palter, bread baked commercially, which is muttar to eat. There is a chumra not to eat it, some people follow this chumra all the time, some follow it only on Shabbos and Yom Tov, but it is only a chumra, halachicly it is completely muttar.