We hear these terms an awful lot as we grow older, because the fact is most people my age(52) will have some degree of insulin resistance, mainly due to our diets and aging.
Insulin resistance is not a disease but a condition in which a person's body cells have a lower level of response to insulin, a hormone secreted by the pancreas that helps to regulate the level of glucose in the body. Therefore, the body produces larger amounts of insulin to maintain proper levels of glucose in the blood.
Although being an apple shape is one of the 4 or so body types, being a really overweight apple shape (big tummy!) is considered a problem, and it serves as a red flag to indicate insulin resistance and all the ills associated with that down the road. It is important when one has that body shape and one is severely overweight, to be responsible and lose the weight - at least to a healthier weight - not necessarily fashionable skinny, which believe it or not, is not that healthy either as one ages. My husband read something the other day that said if one is going into one's seventies at normal weight or below, risk of death at a younger age increases. That's so weird and I'd have to do more research to figure out if that is true.
One of the reasons a low-carb diet works or intermittent fasting (my latest thing) is because it does an end run on the insulin output - it reduces the amount of insulin produced in any given day. Since insulin is the fat storing hormone, this means less fat is stored.