You know what salad is.
Salad is made of green leaves. Actually no, there are lots of other colors, lots of other kinds; and many, such as rice salad, pasta salad, potato salad, include no leaves at all.
In any case, salad is made of vegetables. Actually no: fruit salad.
I meant vegetal, as in non-animal. Actually no: salads often contain cheese, meat, fish, seafood.
In any case, salad is a cold dish. Actually no: did you never try a warm goat cheese salad?
Salad has dressing. Actually no: I know quite a few people who shun dressings.
Salads are consumed at the beginning of a meal. Actually no: in France, the normal place of a salad is after the main course.
At least they are only part of a meal. Actually no: have you not heard of the dinner salad?
Salads have something to do with salt. Actually no: although you are right etymologically, as the word comes through the French salade from the Latin saleta, salty, in our blood-pressure-conscious world the cook often does not put any salt.
Salads are only consumed at lunch. At dinner too. And maybe… I take that back.
I know a salad when I see one. Or maybe when I taste one. Although I have never tried blindfolded.
Then explain to us what it is.
Well, if it says “salad” on the menu it must be a salad.
Can you do better?
I will have to come back to you on that one.
If it is so hard to come up with a convincing definition for such a banal notion (and it is real fun to look at good dictionaries and see the contortions they go through in trying to make some sense of it), no wonder software requirements specifications (SRS) are so hard. One of the obligatory steps in a requirements process — “agile” or not — is to build up a glossary for the project : a set of definitions for the terms of the trade, those words from the problem domain that the stakeholders throw in assuredly all the time in discussions, with the assumption that everyone else understands, except that when you try to understand too you realize there is no clear definition and even, in some cases, different people understand them in different ways.
If definitions are so hard, are requirements then impossible? The trick is that we often do not need a dictionary-style definition of what things are; we only need to know what they have, in other words what are their properties and operations. This is the abstract data type approach, also known as object technology. But it is still hard to convince the stakeholders to explain what they mean.
The German language has one more use of salads: the affectionate term to describe the jumble of wires that mars the back of your desk (I am guessing) and also the front of mine (in this case I know) is Kabelsalat, cable salad . More than a few SRS are like that too: requirements salads.
 IEEE: Standard 830-1998, Recommended Practice for Software Requirements Specifications, available (for a fee) here.
 German Wikipedia: Kabelsalat entry, available here.