Party secretary was a political title, specifically that of a senior official in the National Socialist Party, initially used on 20th century Earth, then resurrected on 23rd century Ekos. Typically the title was below that of Chairman.
Party Secretary Daras, who held the title there in 2268, used her influence in that position to aide in her role as a Zeon sympathizer. As such, it was not questioned when she allowed the Fuhrer's Special Documentary Corps into a top level gathering held at the Ekosian Chancellery. (TOS: "Patterns of Force")