The 'sus' in C sus 2 or F sus 6 or D sus 4 is read as 'Suspended'.

Major and minor chord 

Major chord : root – major 3rd – fifth

Minor chord : root – minor 3rd – fifth

Suspended chords spelling

sus 2 : Root – 2nd – fifth

sus 4 : Root – 4th – fifth

sus 6 : Root – 6th – fifth

In a major or minor chord, instead of the third note, if we use 2nd, 4th or 6th note, we get the corresponding suspended chord.

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