general terminology

principle of superposition

when two or more waves meet at a point, resultant displacement is the sum of the displacement of the individual waves

diffraction

spreading of waves when pass through a gap or around an edge creating a geometric shadow

interference

superposition of two or more waves from coherent sources

constructive interference

2 waves come together to produce an increased amplitude at a point in space

destructive interference 

2 waves cancel out to give reduced or zero amplitude at a point in space 

coherent sources

2 sources with exactly the same frequency and 0 or constant phase difference

path difference

extra distance travelled by one of the waves when compared to the other

interference diagram

constructive interference path difference 

n*wavelength 

destructive interference path difference

n+0.5 * wavelength

interference maxima

regions where light wave from 2 slits arrive in phase with each other…coherent