What does the old man in Huanggu mean?

"Old man near the Yellow Valley" means copying Huang Tingjian's calligraphy.

Huang Tingjian, whose name is Lu Zhi, is a Taoist priest in the valley, a famous writer and calligrapher in the Northern Song Dynasty.

Huang Tingjian's calligraphy is unique and is one of the "Song Sijia".