Instead of just meaning "a lot of", abundance means different things in the scientific community. One definition of abundance is the ratio of the total mass of some element or substance as compared to the total mass of Earth. I guess this could be called geological abundance or something, if that is easier to remember. An example of this form of abundance would be something like "the abundance of aluminum in Earth's crust is 8%" because Earth's crust is 8% aluminum.
Another definition of abundance is the ratio of the number of atoms of a particular isotope of an element compared to the total number of atoms of all isotopes of that element. For example, "the natural abundance of uranium-235 is 0.71%" meaning that 0.71% of a sample of natural uranium is the uranium-235 isotope.