Gravitational waves are a phenomenon predicted by Einstein's theory of general relativity. They are ripples in the fabric of spacetime caused by the acceleration or movement of massive objects. Unlike electromagnetic waves, which are oscillations of electric and magnetic fields, gravitational waves are fluctuations in the curvature of spacetime itself.
Gravitational waves do not have a specific wavelength in the same way that electromagnetic waves do. Electromagnetic waves have a characteristic wavelength associated with their frequency, but gravitational waves can have a range of frequencies. Gravitational waves can have wavelengths ranging from a fraction of the size of an atomic nucleus to cosmic scales, depending on the source of the waves.
Regarding your second question, the term "gravitational waves" is used instead of "gravitational beams" because the term "beam" typically implies a focused or directed flow of energy or particles. Gravitational waves, on the other hand, radiate outward in all directions from their source, much like ripples spreading on the surface of a pond. The term "waves" captures this propagating nature of the phenomenon.
It's also worth noting that gravitational waves are fundamentally different from electromagnetic waves. They are a consequence of the curvature of spacetime caused by mass and energy, whereas electromagnetic waves are the result of oscillating electric and magnetic fields. Therefore, using the term "gravitational waves" helps distinguish them from other types of waves and accurately reflects their nature and origin.