G'day,
quote: "what does the 1d or 2d or 1/2d always mean?"
I feel old ...
what we called a penny was, historically, descended from an ancient Roman coin, called a "denarius". This was abbreviated to "d". Very confusing when I was a boy. Because of a similar history, the abbreviation for pound (= 20 shillings) was "L", for "Librum" (or similar). Shilling was abbreviated to "s", but not because shilling began with "s". No, the shilling was descended from the Roman "solidus".
So, and this will sound hilarious to people born after 1966, "L.s.d." used to be a synonym for "money" generally. As it happens, the other type of LSD became a topic of conversation about the time that decimal currency was introduced.
Back to your legitimate question:
1d = one penny
2d = two pennies, usually written twopence, but pronounced "tuppence". Australia never had a 2d coin, but the Brits did.
1/2d = one-half penny, usually written halfpenny, but pronounced "ha'penny".
The Brits went decimal about 1970. The pound remained the same. The shilling disappeared. The old pennies, etc disappeared. Instead of being equal to 240 old pennies, the pound was now divided into 100 New Pence, which were abbreviated "p", which you have probably heard of. A few years after decimal conversion, the Brits dropped "New Penny/Pence" down to just "Penny/Pence".
Peter