As far as I know, there wasn't any mention of electrons "vibrating" during AQA AS physics last year. If it isn't in the textbook, don't worry about it!
If you're curious though, they are probably referencing quantum mechanics - the concept that particles are "delocalized" when unmeasured. This means that they can't be thought of to have a definite position, as they exist in a superposition of multiple positions at once. Instead, we think of the particle as a "cloud" of probability of where it could be.
If you want to read more, find some articles on "atomic orbitals".