I learned about the spectral hole burning. On Wikipedia, it said
Spectral hole burning is the frequency-selective bleaching of the absorption spectrum of a material, which leads to an increased transmission (a "spectral hole") at the selected frequency.
In that excerpt, does 'transmission' mean 'transparency'? I don't think so, but, I'd like to know exactly difference between transmission and transparency.
Also, in that sentence, what does bleaching mean?