Here's a proposed approximate mathematical definition!
Massive salad (single serving) = over 300 cubic inches (over 5300 cubic cm), weighing over 500g, and containing more than 15 different (tasty) ingredients.
This was based on the following facts:
"Massive" depends on how many people the salad is for. So, a salad might not be so large one shared out between a large party. So, I presume that we could address it as a single salad for one person for just one meal.
Also, going by what many people written, it also means "with a diverse range of many ingredients".
Subsequently, I would combine these learned facts to say, a
"Massive salad" (per person per meal) would contain in excess of 15 ingredients and weigh in excess of 500g. However, with heavier ingredients (as in potato salad or coleslaw), this might not seem so large, so I would also include a volume factor, such as filling a round bowl that is 1 foot (30cm) wide and 3inches (7.5cm) deep.
This equates roughly to over 300 cubic inches (over 5300 cubic cm), weighing over 500g, and containing more than 15 different ingredients - per single serving.
Different foods have different amounts of water content (e.g. boiled potato versus baked potato), so the weight does not necessarily reflect the energy input (Calories or Joules).
If you wonder where I got 500g from, I based it on 2kg over 4 meals per day. But every person is different. Lettuce can take up a lot of volume without weighing much, so mixing lots of extra ingredients together helps make a salad more nutritious, tasty and heavier.
Here is a dietary quote (from www.quora.com/Approximately-how-many-grams-is-one-meal?share=1):
"An adult needs roughly 2 kg (2000 kcal, 8400 kJ) of food and water per day. Eyeballing this handy Dutch government chart that breaks down to:
25% * 2 kg = 500 grams of fruit/vegetable. (fast carb energy moderated by soluble fiber)
25% * 2 kg = 500 grams of cereal/bread/potato. (insoluble fiber bulk)
20% * 2 kg = 400 grams of dairy/meat. (protein energy for repair)
20% 2 kg = 400 ml of water. (hydration)
10% 2 kg = 200 grams of oil/fat. (slow carb energy and lubrication)*"
So if the "Massive salad" is over 500g and contains these proportions of fibre, protein, water, fat, carbohydrates, etc. then it should meet the average person's bodily needs. But bear in mind that a professional athlete would have different needs to a bus driver. So take it all with a pich of salt!