Question

When a lens refracts different wavelengths at different angles, causing the light in the lens that passes through the edges to be slightly dispersed, this is known as:?

Answer 1

The technical name was kinda given in the question, and I'm guessing that's what they want: Dispersion.  It refers to the phenomenon of different frequencies traveling at different speeds through a medium.  This is due to the fact that the relative electric permittivity is a complex quantity that is a function of frequency.  The relative electric permittivity, $\epsilon_{r}$, is related to the speed of the wave in the medium by the relation:
$c' = \frac{c}{ \sqrt{ \epsilon_{r} } }$
Since this speed is a function of permittivity, and permittivity is a function of frequency, speed is a function of frequency.
Probably more info than you needed....