What is an electron?

Particle or wave? Here is a quote from a textbook describing what an electron “is”.

1. Giancoli, Physics 5th edition page 837. We might ask ourselves: "What is an electron?" The early experiments of J. J. Thomson indicated a glow in a tube that moved when a magnetic field was applied. The results of these and other experiments were best interpreted as being caused by tiny negatively charged particles which we now call electrons. No one, however has actually seen an electron directly. The drawings we sometimes make of electrons as tiny spheres with a negative charge on them are merely convenient pictures (now recognized to be inaccurate). Again we must rely on experimental results, some of which are best interpreted using a particle model and others the wave model. These models are mere pictures that we use to extrapolate from the macroscopic world to the tiny microscopic world of the atom. And there is no reason to expect that these models somehow reflect the reality of an electron. We thus use a wave or a particle model (whichever works best in the situation) so that we can talk about what is happening. But we shouldn't be led to believe that an electron is a wave or a particle. Instead, we could say that an electron is the set of its properties that we can measure. Bertrand Russell said it well when he wrote that an electron is a "logical construction".