Basically it means very cold. The sort of cold that puts a heavy frost on the ground and makes your hands go numb. The word is possibly a combination of “frosty” and “hoary”; hoary being the greyish-white appearance frost gives to the countryside.
This is a play on words. Most people say the words on god or on jah. This is a spinoff on the words on jah rooted from the death of late artist xxxtentacion. His full name was Jahseh Dwayne Ricardo Onfroy. Its used the same as on god and on jah.