What is a lungo vs ristretto vs normale espresso?

A ristretto ("restricted") uses less water — about 1:1.5 ratio — producing a very concentrated, sweeter, less bitter shot. A normale is the standard 1:2 ratio (18g in, 36g out). A lungo ("long") uses more water — 1:3 or more — producing a larger, more dilute shot. Ristretto is often preferred in milk drinks for its sweetness; lungo is more similar to strong filter coffee. All three use the same grind and dose but different yield targets.