Strong concentrated espresso; a drink of this; = caffè ristretto.
Espresso ristretto is brewed using the same amount of coffee grounds as is used for ordinary espresso, but with less water, thereby producing a smaller but thicker and stronger drink..
Origin
1980s; earliest use found in The New York Times. Either from Italian espresso ristretto (rare), or independently from espresso + Italian ristretto, after caffè ristretto or its etymon Italian caffè ristretto.