can someone answer me what is the meaning of 低 熱 量 的 小 食 ??

To understand that, you had better understand what 熱 量 means.

When food (carbohydrates or fats) is burnt,
chemical energy stored in them will be released as heat,
which is what we measure.
Therefore, 熱 量 is used as a measurement of
how much energy giving "food" in the snack you are referring to.

To help you understand more, for example, minerals and water
will not be used to provide energy in our body.
So, they are zero calorie.

To answer your question, 低 熱 量 的 小 食 usually refer to snack
that contains less fats 脂肪

snacks with low energy content means that snacks contain
less carbohydrate and less fat.
the energy content is high when carbohydrate or fat content is
high.