Glowstick throws a spinning glowstick toward a nearby target and after a while boomerangs back the way it came from. However, if the hit limit is reached, the glowstick instead explodes in an area.
Minato Aqua's members emote, note the left and right glowstick.
Glowsticks, also known as penlights, are common props in concerts carried by the fans. They are especially important in Asian pop concerts, as coordinated glowstick movement is an expected part of the concert experience.
As Hololive is partially inspired by Japanese Idol industry, as well as having Idol fans among its talents, their concerts also feature mass glowstick coordination, which is what Glowstick is likely referencing.[1]
A more abstract version of this can seen in the form of Glowstick emotes that are a the standard part of any Hololive members emote sets (or any music focus VTubers in general) which are usually spammed during a concert or karaoke streams.
As these emotes are part of a channel paid membership content, non-paying viewers will try to substitute them with other vaguely similar looking emotes such as 🥖Baguette, 🧨Fire Cracker or 🥢Chopstick.