Vigil (noun) – an event or a period of time when a person or group stays in a place and quietly waits, prays, etc., especially at night.

Source: https://www.merriam-webster.com/dictionary/vigil

From “A Hunger Artist” by Franz Kafka

“Sometimes there were nightly groups of watchers who carried out their vigil very laxly, deliberately sitting together in a distant corner and putting all their attention into playing cards there, clearly intending to allow the hunger artist a small refreshment, which, according to their way of thinking, he could get from some secret supplies.”

Vigil is used here to describe the nightly activities of the watchers. This shows that these groups of people go out at night and watch the hunger artist, even though they don’t understand the art.