Can refer to a way of playing slide guitar using a steel or a specialised instrument built for playing in steel guitar fashion. Of the latter there are also several types including:

• lap steel guitar - a square-necked variety of resonator guitar, both acoustic and electric (as shown)
• electric pedal steel guitar

Invented by Joseph Kekuku in Hawaii around 1889, it was originally a 6-string wooden guitar built to be a Spanish guitar, but converted to a steel guitar by inserting a metal converter nut (adapter or extension nut) over the nut at the headstock to raise the strings about a half inch off the fretboard. It was originally tuned A Major low bass (EC#AEAE), which has 3 strings tuned the same as the Spanish guitar.

When first seen in the USA, it did not have a name, but since it was held on the lap and played with a steel bar it became known as a 'lapsteel' which is still much used.

In later years the players of blues, bluegrass, folk and other music took up the instrument, but tuned it more to suit the banjo player, to G Major low bass (DBGDGD), which is still popular in that genre of music to this day. They also referred to the steel guitar as a Dobro, which is not really correct as Dobro is just a manufacturer's name and implies that there are no others (Weissenborn, National, and many others).

It is also sometimes referred to as a slide guitar, which is really not a type of guitar at all but a way of playing a regular Spanish guitar using a metal cylinder slid over the left hand little finger to make a sound imitating the steel guitar. Another misnomer for steel guitar is 'Hawaiian guitar', which on Hawaii is reserved for slack key guitars.

In the 1920s, the first electric instrument was invented, which by the way was a steel guitar. Soon the 6 strings had a 7th string added, then an 8th string, then double necks whether 6 strings or 8 strings each. There are even steel guitars with 4 necks. The pedal steel guitar came along in the 1940s.

The modern electric steel guitar can still be played on the lap, or it can have manufactured legs. The acoustic steel guitar is played on the lap or suspended by a strap so the player can stroll while performing, and it can have an electric pick-up, for amplification.