What is the repeated courtship sound of a male katydid commonly called?

The repeated courtship sound of a male katydid is commonly called stridulation.

Stridulation is sound production by rubbing one body part against another. In katydids, a male typically rubs specialized areas of its forewings together. One wing bears a file-like structure, while the other has a scraper; their movement creates vibrations that become the insect’s song.

Male katydids use these songs mainly to attract females and communicate with potential mates. Each species tends to have characteristic pulse patterns and frequencies, helping females recognize appropriate males. Many katydid songs are ultrasonic or partly ultrasonic, so people may hear only some species clearly.

Stridulation is a broad biological term, not a mechanism unique to katydids. Crickets also stridulate, and some beetles, grasshoppers and other animals make sounds through friction. The exact body structures differ among groups, so “stridulation” identifies the rubbing mechanism rather than one universal sound.