Definition. Compositionality, computability, and complexity › Grammatical term algebra (§ 2.1) [pagin2021-gta]

A grammatical term algebra $G T A_{L}$ of a language $L$ is a partial algebra $⟨ G T_{L}, A T_{L}, Σ_{L} ⟩$ , where—

$G T_{L}$ is the set of grammatical terms for $L$ ,
$A T_{L}$ is a finite set of atomic (grammatical) terms for $L$ , and
$Σ_{L}$ is a finite set of syntactic operations for $L$ . $G T_{L}$ is the closure of $A T_{L}$ under $Σ_{L}$ .

Reference. Compositionality, computability, and complexity [pagin2021]