First, as far as dynasties are concerned, the so-called "Jiankang became the imperial city since the Six Dynasties" in the Biography of Zhang Shou in Song Dynasty refers to Wu, Eastern Jin, Song, Qi, Liang and Chen.
Secondly, as far as the times are concerned, it refers to the entire Wei, Jin, Southern and Northern Dynasties from the Three Kingdoms to the Chen Dynasty, including the large and small regimes established in the north and south of China.
Scholars in later generations said that the Six Dynasties were more about the times than the dynasties. For example, Yan Kejun and A Qing compiled Ancient History of Three Dynasties, Records of Three Kingdoms in Qin and Han Dynasties and Records of Six Dynasties. In the Six Dynasties, there were not only all Wen Song and full-text Qi, but also all Hou Huiwen, all North Wen Qi, all Zhou Wen and all Sui Wen. In the general history of literature, it is called "Han, Wei and Six Dynasties", that is, it is based on this theory.
But now historians pay attention to the Six Dynasties when Jiankang (Nanjing) was the capital. For details, please refer to Records of Six Dynasties (Jiangsu Ancient Books Publishing House) edited by Zong. Before that, Mr Wu Ze, who just died in our department, talked about the Six Dynasties in a broad sense and the Six Dynasties in a narrow sense. You can also refer to the historical manuscripts of the Six Dynasties compiled by three teachers in our department: Jane, Zhuang Huiming and Zhang Yi.
Generally speaking:
The six dynasties in history refer to the Wu, Eastern Jin, Song, Qi, Liang and Chen dynasties with Nanjing as their capital.