What does the dg fd reg mean on a one penny coin?

Answer 1

It's part of a heavily abbreviated Latin phrase that appears on all British Coins and most coins from the British Empire / Commonwealth.

Depending on the size of the coin the abbreviation may be shorter or longer, but you'll usually see something like "Georgius VI D. G. Britt Omni Rex Fid Def Ind Imp" which translates to the mouthful "George 6th, By the Grace of God King of All Britain, Defender of the Faith, and Emperor of India".

REG or REGINA = Queen

REX = King

Answer 2

D G REG F D has appeared on British coins and the coins of many of the British Empire/Commonwealth coins in various forms and degrees of abbreviation for donkeys years.

D G or DEI GRATIA is Latin for "by the grace of god".

REG or REGINA is Latin for Queen (REX for King)

F D or FID DEF or FIDEI DEFENSOR is Latin for "defender of the faith".

They are all part of the impressive title of the reigning British Monarch although the legend changes periodically as the state of the British Empire/Commonwealth changed.

A particularly spectacular version of the legend can be found on later coins from the reign of Queen Victoria -

The phrase "VICTORIA DEI GRA BRITT REGINA FID DEF IND IMP" is mostly abbreviated from Latin. The literal definition is - "Victoria by the Grace of God, Queen of the British territories, Defender of the Faith, Empress of India".