Sometimes a recipe I've found online specifies Kosher salt. I've never been able to find that here in NZ, so finally searched for alternatives.
Two videos were very helpful, explaining it mainly just means flaky salt.
Do I Need to Use Kosher Salt?:
Regular table salt is comprised of many minute, regularly shaped cubes.
Kosher salt … forms large, craggy flakes that don't fit together very well.
A cup of table salt will have twice the salting power of a cup of Diamond Crystal kosher salt
See also: What is kosher salt, and why do (American) chefs love it?.
Off to buy flaky salt.