bottleneck
n. B2 Upper Intermediate US //ˈbɑtəɫˌnɛk// UK //bˈɒtəlnˌɛk// bot·tle·neck
n. a part of a process where things get stuck and move much slower than the rest. In music, it can also describe a specific part of a song that is very difficult to play.
n. a point in a process where the flow of progress is significantly slowed or stopped. In a musical context, it refers to a technically demanding section of a piece that requires great skill to perform.
The final chorus is the real bottleneck of the song.
The band struggled with the bottleneck of the guitar solo during their first live performance.
While the rest of the album flows smoothly, the final movement acts as a bottleneck, testing the endurance and technical precision of the entire orchestra.
From bottle + neck.