The Standard Model defines electron as a point particle having radius zero. All elementary particles in the SM are point-like. This can be a problem because they can become infinitely close to one another, which causes Feynman diagrams with loops to blow up. These infinities can be solved by physicists using very small distances to reduce the integrals. It is as though particles have a radius. This could be interpreted as an indication that electrons may be composed of smaller particles (or strings). The electron would have a radius in that scenario, just like other composite particles such as a proton.