What does this notation mean in schematic design?

I'm sure we all have anecdotal stories of hearing music better than many live performances with padded rooms with massive planar arrays or 2.5 m tall electrostatics or a 250 kW US festival live with massive arrays of 1m speakers in stereo or being able to hear the 2nd violinist turn a page on a direct-cut album from Deutche Grammaphone. Then life changes priorities and you have no time or money to upgrade. Now I'm satisfied with a Yamaha 2.1 system on my TV/ PC display while others are happy with their 300W Class D stereo.