The quantitatory descriptor plural is the form of a noun that serves to indicate that the quantity of that noun is larger than one.
The quantitatory descriptor singular is the form of a noun that serves to indicate that the quantity of that noun is one. Being singular means the noun is a mathematical unit of "one".
In some languages, a suffix (word ending) is added to a word to show that the word means two or more than two. In the English language, the suffix_ -s is used to indicate that a noun has been inflexed into its plural form. Here is an example_ cat is a singular noun, but cats is a plural noun.