On a label, "sugar" means all free sugars — added sugar plus the sugars in fruit juice, honey and jaggery. Your body treats them the same way; the WHO groups them together for exactly this reason. 4 grams is one teaspoon.
Sugar rarely appears once in an ingredient list. Sucrose, glucose, fructose, corn syrup, invert syrup, maltodextrin, fruit juice concentrate, honey and jaggery are all free sugars — a product can list four of them and each lands lower in the ingredient order than "sugar" alone would.
"No added sugar" is not "low sugar". A 100% fruit juice can carry 10+ g of sugar per 100 ml — comparable to a soft drink — with nothing "added" at all.
"Sugar-free" governs sucrose, not carbohydrates. A sugar-free biscuit is still mostly refined flour, which digests to glucose.
Per-serving numbers can make sugar look small: 6 g "per biscuit" reads gently; 32 g per 100 g is the same product.
Sugar per 100 g/ml is a weighted input to the negative load. We always score per-100 — never the brand's chosen serving — so shrinking the serving printed on the pack cannot move the score.