Gelli is a former coal mining village which is a district of the community of Ystrad.

The village of Gelli takes its name from a farm that was once found in the area, which translates from the Welsh language roughly as 'small wood or copse'.

A lengthy archaeological report was published in 1906,[1] but little remains of the site, with much destroyed during the construction of the Nant y Gwyddon refuse tip.

[2] Gelli (Nantgwyddon) was also home to a landfill site which has been at the centre of controversial reports connecting it with birth defects in children born in the nearby vicinity.

[6] Ysgol Gyfun Gynradd Bronllwyn is a Welsh medium primary school serving Gelli and surrounding area.