A laser beam was a coherent shaft of light. When referring to light (or any other wave pattern for that matter), coherence referred to the pattern's uniformity in multiple waves. In other words, each light wave emitted from the laser device had the same wavelength and amplitude as all other waves emitted from the same device, and all "crests" and "troughs" of every wave were aligned with the others.
Lasers were generated by stimulating a "gain medium"; this substance was charged with electricity, radiation or even by chemical reaction so as to release energy in the form of photons. The gain medium could come in the form of a solid (often a crystal), liquid or gas (tibanna gas was reputedly a favored medium). The "gain medium," when charged, saw the rapid excitement of its constituent atoms. These atoms would experience increases in electron energy levels. Said electrons, seeking equilibrium, then released photons, or packets of electromagnetic radiation, so as to self-stabilize. The produced radiation, reflected and amplified by the optical cavity, could then be released as a high-powered and potentially destructive beam of coherent radiation. The output coupler was responsible for the release of the beam from the optical cavity.
There is clearly a difference between lasers and blasters, and blasters are clearly the modern technology.