phonotactics

This term refers to the specific constraints of a language that dictate which sounds can appear next to each other and where they can occur within a syllable. It is a technical term used primarily in linguistics and phonology to describe the structural "grammar" of sounds, distinguishing between permissible sequences and those that are phonologically illegal in a given tongue.

Grammatically, this word is a mass noun that functions as a singular entity despite its -s ending, similar to other academic disciplines like mathematics or physics. It describes a field of study or a set of rules and is therefore treated as uncountable in standard linguistic discourse.