* Mechanical waves require a medium: Mechanical waves need a material medium (like water, air, or a solid) to travel through. They involve the oscillation of particles within that medium.

* Electromagnetic waves don't need a medium: Electromagnetic waves can travel through a vacuum, like the vast expanse of space. They are composed of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.

Examples:

* Mechanical waves: Sound waves, waves on a string, seismic waves.

* Electromagnetic waves: Light, radio waves, microwaves, X-rays, gamma rays.

In summary: The key difference lies in the requirement of a medium. Mechanical waves need it, while electromagnetic waves do not.