Although it sounds moderately peculiar, Young's Slits is actually referring to Thomas Young's double slit interference experiment.

This experiment had historical significance as it was undeniable evidence of the wave nature of light. (See: wave particle duality/quantum mechanics)

In this experiment a point source of light generates coherent wavetrains which pass through two equally sized slits to form a rapid falloff pattern of fringes on a viewing screen.

The effect of changing various variables in this experiment can be predicted with the followind formula:

λ/S = Y/X
λ is wavelength of the light source.
S is the slit seperation.
Y = seperation of fringes on the screen.
X = Distance between slits and screen.

In a practical experiment there is in fact an initial single slit, before the double slit, to act as an approximation to a point source of light. (In order to provide coherent wavetrains!)