* Heol: Sun
* Y: The
* Dinas: City
It could also refer to a specific place. There is a place called "Heol Y Dinas" in the village of Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch on the Isle of Anglesey, Wales.
Without further context, it's impossible to know for sure if the phrase is referring to a specific location or just a general phrase meaning "The Sun of the City."