Although there is striking variation across languages (and even within a single language) in how the plural is formally expressed, it is relatively easy to indicate what plurality is from a morphological point of view: the plural is one of the instances of the inflectional category of number. From a semantic point of view, however, the concept of plurality is much more diffuse. To start with, the general folk linguistic intuition that being plural expresses being more than one is inaccurate. For example, while (1a) suggests that there are multiple stains on the carpet, (1b) does not suggest that only the carrying of multiple guns is illegal, nor does (1c) suggest it might be the case that there has been a solitary alien walking the earth.
a. There are stains on the carpet.
b. Carrying guns is illegal in Illinois.
c. No aliens have ever walked the earth.
Furthermore, plurality may emerge from sentences that lack any plural morphology, such as the first sentence in (2). Despite the morphologically singular a picture, this sentence expresses that a multitude of pictures was drawn, each by one of the boys. This emergent plurality becomes apparent in the second sentence in which a plural pronoun refers to the pictures that the boys drew.
2) Each boy drew a picture. They are hanging on the wall.
It is often said that in languages like English (and indeed Indo-European languages, generally) plurality is an essentially nominal phenomenon. Corbett (2000), for instance, uses (3) to point out that the plural verbal form must be an uninterpreted agreement reflex triggered by the (unmarked) plurality of the noun. We cannot, for instance, use (3) to express that a single sheep drinks from the stream more than once. It has to mean that there were multiple sheep.
(3) The sheep drink from the stream.
In other languages verbal number marking does have semantic substance. For instance, (4), an example from Hausa (from Součková, 2011), is incompatible with there being a single kick to the table and typically expresses a quick repetition of kicks. This interpretation is triggered by plural morphology, namely. partial reduplication of the verb stem.