A variable noun is one that can be "varied" (changed or added to). In English most nouns are varied in order to construct plurals. An example invariable noun is "sheep", which does not change in the plural.
sorry for digging up this old thread, but I stumbled across it while researching different classes of nouns. Thought it would be a good opportunity to stop leeching and to finally register & contribute.
Invariable nouns can have either singular or plural form (e.g. information, scissors)
They are invariable in that sense that they only have one number, singular or plural.
Variable nouns have a singular and plural form. (house-houses)
And there are also nouns which can be both variable and invariable (e.g cake)
So sheep is actually a variable noun, because it has a singular and plural form (zero-plural).
Within those 3 classes of nouns one can distinguish even more sub-classes, but I think that this is the basic concept.
Variable Noun is a word which changes its form with reference to the quantity / number talked about in a sentence. Thats when we get the derivation as singular noun or plural noun.
e.g: a shop (singular)
three shops (plural)
Words like music, scissors, Netherlands are Invariable Nouns as their form remains constant irrespective context. Ofcourse Invariable noun is further broken down in various forms and studied in details.