Csus9 chord. The full formula C7sus4(9) can be seen as “analytic notation” that shows all the chords ingredients, but normally you'll just write Csus9 or C9sus. Very common and important chord in pop and soul music. Csus9 will often replace the dominant 7th chord C7.
The sus9 chord is a 7sus4 chord with an additional 9th. You can get the 9th by going up a major second (= 1 whole-step = 2 frets) from a root C to D. It will be written as 9 and not as 2, because it extends the chord rather than modifying the basic structure of root, 3rd and 5th (like in a sus2 chord, where the 2 replaces the 3rd and therefore is notated as 2 together with the abbreviation sus).
The Csus9 chord contains the tones C (1), F (4), G (5), Bb (7) and D (9).
Because the 5th is often omitted in this chord, you can consider and notate it as slash chord: instead of Csus9 you can write Bb/C, a Bb major chord (consisting of Bb, D and F) over the bass note C.
Example chord progressions: FF/ABbmaj7 Csus9 Dm7 G7 Csus9 F Dm7 Am7 BbCsus9