According to our current understanding of physics, specifically within the framework of special relativity, the maximum velocity that something with mass can theoretically achieve is the speed of light in a vacuum, denoted by "c."
Einstein's theory of relativity states that as an object with mass approaches the speed of light, its energy and momentum increase without bound. However, it would require an infinite amount of energy to accelerate an object with mass to the speed of light, which is considered impossible.
As an object with mass approaches the speed of light, its relativistic mass increases, and the energy required to accelerate it further also increases. At the speed of light, an object with mass would require an infinite amount of energy to accelerate any further, which is physically unattainable.
Therefore, the speed of light in a vacuum is often considered to be the ultimate cosmic speed limit. It plays a fundamental role in many aspects of physics and has been experimentally verified to be the same for all observers, regardless of their relative motion.