Slack-key guitar is a fingerstyle genre of guitar music that originated in Hawaii. This style of guitar playing involves altering the standard tuning on a guitar from E-A-D-G-B-E, which has been used for centuries, so that strumming across the open strings will then sound a harmonious chord, typically an open major. This requires altering or "slacking" certain strings, which is the origin of the term "slack key". The style typically features an alternating-bass pattern, played by the thumb on the lower two or three strings of the guitar, while the melody is played by the fingers on the three or four highest strings. There are as many as fifty tunings that have been used in this style of playing, and tunings were once guarded fiercely and passed down as family secrets. In the early 20th century, the steel guitar and the ukulele gained wide popularity in America, but the slack-key style remained a folk tradition of family entertainment for Hawaiians until about the 1960s and 1970s during the second Hawaiian renaissance.

A steel guitar is any guitar played while moving a steel bar or similar hard object against plucked strings. The bar itself is called a "steel" and is the source of the name "steel guitar". The instrument differs from a conventional guitar in that it is played without using frets; conceptually, it is somewhat akin to playing a guitar with one finger. Known for its portamento capabilities, gliding smoothly over every pitch between notes, the instrument can produce a sinuous crying sound and deep vibrato emulating the human singing voice. Typically, the strings are plucked by the fingers of the dominant hand, while the steel tone bar is pressed lightly against the strings and moved by the opposite hand.