In this score for harp, there's this weird symbol: (outlined in red)
I have no idea what it means, is it some kind of glissando?
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The overlaid circle and plus generally mean damping a string. Combining that with small noteheads and a range shows which strings to damp. Harmonically this makes sense here, to prevent those low strings, plucked in the previous bar and a half, from polluting the C major chord that follows.
Here's another example of exactly that symbol, along with variations.