A well drink, also called a rail drink, is made with the house brand of liquor. It's called a well drink because the low-cost liquor is kept in the well at the bar.
Meanwhile, if you "call out" a specific liquor brand for your mixed drink like an Absolut and soda, you'll get a higher quality liquor, which also means paying a higher price.
Some premium bottles are classified as top-shelf, which is a step up from call liquors in quality and price — this is why they are stored carefully on a high shelf.
Keeping in mind that each bar has its own fee structure, some examples of top-shelf liquors include Grey Goose, Bacardi 151, Patron, Crown Royal, and Makers Mark.