It refers to Pedal Bass

Type Alt-F5 on the chord, and select Pedal bass, In your case it is probably something like Pedal Bass on beat 2 & 4 with bass of G for 2 bars.

from the help: "Pedal Bass is a repetitive figure played by the bass on the same root note (e.g., often the fifth of the scale) during a chord progression. You can set the bass part to play a pedal bass at any bar for a range of bars. For example, you could set the bass to pedal on a G note, on beats 2 and 4, throughout a chord progression for 4 bars, i.e., C6 | Ebdim | Dm7 |G7. This is useful for intros, interludes, and endings of choruses."

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