The trp operon is said to be:

The trp operon is said to be a repressible operon because its transcription is usually ON but can be inhibited (repressed) when a specific small molecule (in this case, tryptophan) binds allosterically to a regulatory protein.

Lac operon is an inducible operon as it is usually off but can be stimulated (induced) when a specific small molecule interacts with a regulatory protein.

Regulation of both the trp and lac operons involves both positive and negative control.

The trp repressor is the protein product of a regulatory gene called trpR, which is located some distance from the trp operon and has its own promoter.