It means it was minted at the Philadelphia mint.boooy
It is the date it was minted (made).
It means that the coin is rare. For example a 1909-S VDB cent is a key date. This coin is rare.
7 Sides on a Twenty Pence Coin
If you mean a mint mark on the reverse of the coin, it's a D or S but not a P. Please look at the coin again.
It's a mintmark, showing which mint made the coin. An S is the San Francisco mint a D is Denver. The P is for Philadelphia and is only on coins made from 1980 to date except the penny it has never had a P mintmark.
You need to give the denomination and date of the coin. Also where you see the 77 at on the coin.
The "P" mintmark was used on 1980 to date Kennedy halves so it don't matter what the date is, it's just 50 cents, spend it.
S and P aren't grades, they're mint marks indicating where a coin was struck. There are many other possible mint marks for U.S. coins as well, depending on their denomination and date.
From 1793 to date the mint has NEVER used a "P" mintmark on any one cent coin.
If you mean one of the Sacagawea dollars or a Presidential dollar the date is on the edge of the coin and its not gold.
A date set is one coin from each year that type of coin was made using the most common highest mintage lower value coins.
its a mint mark, the letter indicates where the coin was made P = Philadelphia, D = Denver