What is Half Dollar?

Legal Definition
The term Half dollar may refer to a half-unit of several currencies that are named "dollar". Normally, $1 is divided into 100 cents, so a half dollar is equal to 50 cents. Coins and/or banknotes of that amount are as such denominated at a value of 50 cents. More than a dozen countries are known to have their own unique dollar currency, out of these not all use the 50 cent piece or half dollar.
-- Wikipedia
Legal Definition
Money. A silver coin of the United States of the value of fifty cents. It weighs two hundred and six and one-fourth grains. Of one thousand parts, nine hundred are of pure silver, and one hundred of alloy. Act of January 18, 1837, S. 8 and 9, 4 Sharsw. cont. of Story's L. U. S.2523, 4. Vide Money.
-- Bouviers Law Dictionary
Legal Definition
A silver coin of the United States, of the value of fifty cents, or one-half the value of a dollar.
-- Black's Law Dictionary