Final answer:
Combinatorial control is the process by which multiple transcriptional regulators determine a gene's expression level. An operon that produces proteins consistently at intermediate levels is referred to as constitutive.
Step-by-step explanation:
Many transcriptional regulators function together to decide the expression level of a particular gene. This complex mechanism is referred to as combinatorial control. This concept is different from operons, repression, and activation, which are other forms of gene expression regulation. An operon that is transcribed and translated continuously providing constant intermediate levels of protein products without further control is described as constitutive.