Both. The latter is more archaic than the former.
In English, "50 cents" can be simply referred to as "fifty cents." It is often abbreviated as "50¢" or referred to as "half a dollar." In some contexts, it might be colloquially called "a half-dollar," though a half-dollar coin is actually worth 50 cents in U.S. currency.
A 1951 Franklin half has a value of abut $15.00.
Because it's been professionally graded, it could be worth a few dollars. Being that it's only a 1978-D half dollar, it's not an especially valuable coin.
25 000
First off, WHY DO YOU HAVE A TWO AND A HALF DOLAR GOLD PIECE??!?!?!?!?!?!?!?!!
Half a dollar
One half dollar (50 cent piece) and two quarter dollars (25 cent each piece)
No Kennedy half-dollar from 1971 to date made for general circulation contains any silver.
It's called a Half Dollar or a Kennedy Half Dollar
Current Circulation Coins: One cent - no correct other name, but often colloquially called a "penny" Five cents - "nickel" Ten cents - "dime" Twenty-Five cents - "quarter" Fifty cents - "half dollar" Dollar - "buck" Susan B Anthony dollar coins were often times called "Carter Quarters", large sized dollar coins including the Eisenhower dollar which contains no silver is often called a "Silver Dollar" and Sacagewea and Presidential Dollars are often called "Golden Dollars" even though they contain no gold and should be distinguished from the much smaller and older Gold Dollar (1849-1889) that was struck in real gold. Historical Gold Coins: $1 - "Dollar" $2.50 - "Quarter Eagle" $3 - "Three Dollar Piece" $4 - "Stella" $5 - "Half-Eagle" $10 - "Eagle" $20 - "Double Eagle" Historical Coins: 1/2 Cent - "Half-cent piece" 2 Cents - "Two-Cent piece" 3 Cents - "Three-Cent Piece" (often called "trimes") 5 Cents (when struck in silver) - "Half-Dime" 20 Cents - "Twenty-Cent Piece" or "double dime"
Two half-dollars otherwise known as a fifty cent piece make a dollar.
Here you go, the 1918 half dollar is called the Walking liberty half dollar. http://www.coinconcierge.com/images/1918swalkerfobv.jpg