Counter
はく
4分の4拍子の曲では、通常、1拍目と3拍目の頭に強拍が来ます。
For music in four-four time, the stress usually comes to a head at the first and third beats.
This counter is used to count musical beats when you're listening to or playing music.
This has the same reading as the kanji you learned, meaning you know the reading!