What is "comet seeker"

A comet seeker is a type of small telescope adapted especially to searching for comets: commonly of short focal length and large aperture, in order to secure the greatest brilliancy of light.

For example, in 1842 a 4-inch (10 cm) aperture Comet Seeker was added to Markree Observatory, which was used to discover 9 Metis in 1848.