I don't yet own dslr lenses, perhaps another should chime in, here. All this is from reading ads and forums.
There are consumer lenses, usually like your "kit" lens. Adequate, perhaps does some things well. $85 - $150
A step up lenses. Sharper, but also more specialized. Still, not "professional" glass. $150 - $400. A lot of semi-serious hobbyists talk about these.
"Professional" lenses. If you go to your camera rental houses, these are the lenses they rent to the pros for contract shoots. They include "L" lenses. Customers like magazines, advertising, etc, demand crispness and good composition. These lenses, so the forums state, deliver. $500 and up.
"L" glass is another class of pro lenses. Usually, from what I see of the ads, specialized. Something about the chemistry of the glass helps the predictability of the refraction, aids in clarity, and cuts down on chromatic aberration. Like aviation gasoline doesn't make a motor more powerful, but it allows engineers to tweak the motor to get a better power to weight out of it.
(big grin) Also, think of the "L" standing for (L)ow bank account, or (L)ess savings.
There are lenses whose ads claim to be as good as "L". Maybe they are. I probably will never know. Way outta my price range.
A sign in a speed shop in Brooklyn, MD in 1976, "Speed costs money, son. Just how fast do you want to go?" Just how crisp, clear and sharp do you need your photos to be? If you are doing 12' x 30' murals from your photos ...