What is diffraction grating?

Diffraction Gratings are optical components used to separate light into its component wavelengths. Diffraction Gratings are used in spectroscopy, or for integration into spectrophotometers or monochromators. Diffraction Gratings consist of a series of closely packed grooves that have been engraved or etched into the Grating's surface. Diffraction Gratings can be either transmissive or reflective. As light transmits through or reflects off a Grating, the grooves cause the light to diffract, dispersing the light into its component wavelength.

What is blazed grating?
When the grating is carved into a zigzag groove section, the light energy of the grating is concentrated in the predetermined direction, that is, at a certain spectral level. When you look in that direction, the spectrum is at its maximum intensity, and that's called a blaze.