From the dictionary:
sal·ad /ˈsaləd/
Noun
1 A cold dish of various mixtures of raw or cooked vegetables,
usually seasoned with oil, vinegar, or other dressing: "a green salad".
2 A mixture containing a specified ingredient dressed with mayonnaise: "tuna salad".
Usually, my emphasis, doesn't mean always.
The Wiki goes on to narrow it down to at least three different ingredients and a 'dressing'.
Salad is a category of dish which basic ingredient is usually raw vegetable. Salad is
often served with a sauce or dressing including oil and an acid as a light savory dish, with a minimum of three ingredients.
http://en.wikipedia.org/wiki/Salad
Often - my emphasis, doesn't mean always.
Personally I consider a salad a mix of fresh (raw) fruits and or vegetables that are served bite sized and with a fork or other utensil. Thus a 'fruit salad' can contain bit sized pieces of fruit without a 'sauce' or seasoning added.
I think originally the dish was tossed greens (lettuce, spinach, type greens) served with vinegar, oil, salt and potent herbs - much like a Caesar Salad. Pretty much a specific dish that over the years has come to include a style of preparing foods over a specific dish influenced by many cultures who had their own ideas how to mix up a bowl of fresh veg and make various 'dressings' (salad sauces).
Technically I can't find anything to exclude a simple cold dish of mixed veg as being 'salad'.