What does k represent and what values does it take? Young double slit intensity.

[Fjolvar]

http://www.phy.davidson.edu/FacHome/thg/201s06_files/Diffraction%20and%20Spatial%20Filtering/double17.gif

http://www.phy.davidson.edu/FacHome/thg/201s06_files/Diffraction%20and%20Spatial%20Filtering/double16.gif

http://www.phy.davidson.edu/FacHome/thg/201s06_files/Diffraction%20and%20Spatial%20Filtering/double15.gif

Is this just the wave number? 2pi / lambda?