Price Change 24h
PRICE_CHANGE_24H refers to the change in price over the past 24 hours. Suppose, the price of a coin was $100 yesterday and it is $110 today. Since the increase is $10, PRICE_CHANGE_24H is +$10.
This is a good indicator is how volatile a certain cryptocurrency is from day to day. Related terms include PRICE_CHANGE_PERCENTAGE.