Gintable's answer is unfortunately an excellent example for why the concept of "Relativistic Mass" should never be used, and in fact is never used by actual scientists. Unfortunately, the concept survives in elementary textbooks and programs on the science channel because some deluded physics teachers think that it makes learning Relativity easier. But what it actually does is give the student a false, semi-Newtonian misunderstanding of the theory.
Radiation pressure is not evidence that light has mass: it's evidence that light possesses momentum. What a poor physics instructor will do at that point is then say, "...and Newton shows us that momentum is mass times velocity, so if the photon has momentum, then it must have mass." But the problem is that SR is a *replacement* for Newton's Three Laws, which are not correct at speeds near that of light. So no appeal to Newtonian physics is EVER permitted in Relativity, and that line of argumentation is void. What a Relativist says is: "There exists a quantity, the 4-momentum, that transforms as a vector under Lorentz transformations. This quantity's components turn out to be the observed energy and momentum of the particle, and its norm is the mass. Since a photon's energy and momentum are equal, and the norm is m^2=E^2-p^2, the particle has no mass."
A PHOTON HAS NO MASS. When a physicist says "Mass," they mean "Rest Mass," because "Relativistic Mass" stopped being used in physics in 1935.
Gravitational bending of light is not evidence for mass. Only Newtonian gravity describes gravity as the interaction between masses; General relativity does not. It turns out that Newton was wrong about that; his theory of gravity is a good approximation to GR, the correct theory, but it is wrong. Gravity turns out not to be the attraction of masses, but the bending of spacetime, and the source of the bending of spacetime is energy, momentum, flux, pressure, and stress, NOT mass. Once the curvature is produced, all bodies, regardless of their mass, follow the curvature, even if the mass is zero.
A PHOTON HAS NO MASS. When a physicist says "Mass," they mean "Rest Mass," because "Relativistic Mass" stopped being used in physics in 1935.
"Relativistic Mass", meaning, the mass you get when you naively plug in energy into E=mc^2, rather than into the correct equation, E^2 = (mc^2)^2 + (pc)^2, is meaningless. It is NOT the inertia of the particle, i.e. NOT what you would get from observing a force, an acceleration, and dividing one by the other. It is NOT the source or coupling to gravity, which is stress-energy, NOT mass. It is nothing but an attempt to allow students to retain their naive semi-Newtonian heuristics so that the teachers don't have to teach so much. It leads to misconceptions and a poor, shallow understanding of the theory. Don't use it.