Can someone tell me what the difference is between a skein a ball and a hank?
Whats the difference
“Skein” and “ball” are often used interchangeably. A “hank,” however, is rarely wound into a useful…sorry…ball of yarn.
Hanks are one reason knitters/crocheters purchase yarn ball winders or have the shop wind balls for them, if that service is offered.
If you’re looking at a pattern which calls for X skeins/balls of yarn, and you don’t have that exact yarn available, look at the total number of YARDS of yarn needed. That’s where the heart of the matter lies. 
DCM
The pattern that Im looking at calls for 5 hanks, at 100g (82yds) each
A hank is also called a skein so they all mean the same thing, they’re just shaped differently. A skein is a big loop of yarn that needs to be wound in a ball. If you’re going to substitute, use the yardage of a similar type of yarn. It sounds like a super bulky and you’ll need about 410 yds total.
They are used interchangeably, but I think this is what people often think of when the terms are mentioned. Yardage is what counts though when getting enough yarn for a pattern.