Melon is a type of large, sweet, and juicy fruit with a hard rind. It can be referred to as countable when talking about specific melons or uncountable when referring to the fruit in general.
[N-VAR 可变名词]瓜；甜瓜 A melon is a large fruit which is sweet and juicy inside and has a hard green or yellow skin.
Oxford
melon/ˈmelən; NAmEˈmelən/noun[countable , uncountable ]a large fruit with hard green, yellow or orange skin, sweet flesh and juice and a lot of seeds 甜瓜；瓜◆a slice of melon一片瓜☞see also