The standard English name for the instrument is the double bass while it's Italian name is contrabasso, known as contrabass. Depending on the type of music being played, the bass has many other names such as string bass, upright bass, standup bass, acoustic bass, bass violin, doghouse, bull fiddle, hoss bass, and bunkhouse bass.
The bass is widely played in classical symphonies, but also in other genres such as jazz, blues, rock and roll, and bluegrass.
The bass is the largest and lowest pitched bowed string instrument used in modern music today. The typical length of the bass is 78 inches and the bow is 26 inches. It has four strings which are tuned to E, A, D, and G with E being the lowest pitch and G being the highest. The E is the far left string on the diagram and the G is the far right string. The bass is the only standard string instrument tuned in perfect fourths instead of perfect fifths.
The photo to the left shows the structure of the double bass. The top is called either the top or the table and is made of solid spruce while the back called the back is made from solid maple. The sides are called the bouts and contain an upper bout, "C" bout, and lower bout and combine to form the rib structure which are made from a thin maple veneer typically cut from the piece used for the back. The rib structure is joined inside the instrument by spruce blocks known as the end, neck, and corner blocks. The piece connecting the body of the bass to the head is called the neck, which is solid maple glued to the spruce block of the bass body. Glued on top of the neck is the fingerboard where the strings rest and is made of solid ebony. The top of the bass is called the scroll and has a hollowed out center called the pegbox which holds the nut and the metal tuners. The nut is where the strings sit as they come out of the pegbox which is also made of solid ebony. The bridge, made of solid maple, lifts the strings up and causes tension in the strings which are then mounted to the tailpiece, made of ebony. The tailgut, a strong aircraft cable, attaches the tailpiece to the endpin, made of metal, which allows the player to adjust the height of the instrument. The tailgut
attaches to the bottom of the tailpiece and curls over a piece of black ebony at the bottom of the top called the saddle. The saddle loops around the end of the endpin and secures the tension. The most important parts of the instrument are inside the bass: the soundpost and the bass bar. The bass bar is a long and slender spruce bar that is designed to specifically fit the bass between the E and A strings. It is needed for structural and sound purposes. The sound post is a spruce dowel that is tension fit and placed at a certain spot on the inside of the instrument to adjust for sound. The "f" holes are used to amplify the sound.
Above photo from bassmusicianmagazine.com
The bass can either be played with a bow, arco, or by plucking the strings, pizzicato. There are two types of bass bows shown in the bottom left photo. The main difference between the bows is the handhold, as shown on the bottom right. The part of the bow that you hold is called the frog; the French bow is gripped with an overhand grip on the frog and the German bow is held with an underhand grip. The way the bow is held typically makes the French bow better for finesse and the German bow better for power because you can apply more pressure with less tension with a German bow.
Photo from gollihurmusic.com
Top: German bow
Bottom: French bow