Morph, morpheme, allomorph and zero morph

Note that any language has a register of morphemes, the physical realizations of which are called morphs. While morphemes remain ideal abstract units, the corresponding morphs may show some variation. In the case of the plural morpheme, various realizations are possible. These variations sound and look differently:

/z/ in "dogs, beds";
/s/ in "cats";
/iz/ in "garages"

All three morphs are different representations of the same morpheme of plurality. Several morphs that belong to the same morpheme are also called allomorphs: variants of one morpheme. In morphological transcription, morphs are commonly put in between braces. The plural morph in "cats" thus becomes {cat}+{s} in morphological transcription.

A zero morph is a morph, consisting of no phonetic form that is proposed in some analyses as an allomorph of a morpheme that is ordinarily realized by a morph having some phonetic form

The plural form that is realized in two sheep is Ø, in contrast with the plural -s in two goats.