The concept of wavelength applies to particles as well as waves, but it is important to note that the wavelength of a particle is related to its momentum through the de Broglie wavelength equation: λ = h / p, where λ is the wavelength, h is the Planck constant, and p is the momentum of the particle.
The reason an electron can have a larger wavelength than a macroscopic object like a tennis ball is due to its much smaller mass and momentum. The momentum of a particle is related to its mass and velocity, and since an electron has a much smaller mass compared to a tennis ball, it can have a relatively higher momentum for the same velocity.
According to the de Broglie equation, a higher momentum results in a shorter wavelength. So, since the electron has a smaller mass and a higher momentum compared to a tennis ball with a much larger mass, the electron will have a larger wavelength. In other words, the de Broglie wavelength of a particle is inversely proportional to its momentum, and since the momentum of an electron can be significantly higher compared to a macroscopic object like a tennis ball, its wavelength can be larger.