Strings: String instruments produce sound when their strings vibrate.

Bow: A long strip of wood and horsehair, typically used to play string instruments
Violin: The smallest and most versatile of the string family. Held between the shoulder and chin.
Viola: Slightly larger and lower than a violin; also held between shoulder and chin.
Cello: Similar in shape to the violin and viola, but much larger. Played vertically, resting partially on the floor.
Double Bass: Even larger than a cello; also played vertically.
Guitar: A versatile, 6-stringed instrument, usually played with the fingers or a pick, rather than a bow.
Ukulele: Similar to a guitar, but smaller, with four strings.
Banjo: A plucked or strummed string instrument common in folk music.

Woodwinds: Woodwind instruments make sound when a player blows a vibrating column of air through them.

Mouthpiece: The piece on the end of a wind or brass instrument, into which the player blows.
Reed: A thin strip of material that vibrates to produce sound on a woodwind.
Double Reed: Two reeds bound tightly together. Both vibrate to produce sound.
Flute: A long, thin pipe-like instrument. Typically made of metal or wood. It uses no reed.
Clarinet: A long, usually wooden instrument with a single reed.
Saxophone: An S-shaped, metal woodwind instrument with a single reed and a jazzy sound.
Oboe: A double-reeded instrument similar in appearance to the clarinet. Usually made of wood.
Bassoon: A large, long, double-reeded instrument with a deep sound. Usually made of wood.

Brass: Brass instruments are usually made of brass metal. They produce sound when the player's lips vibrate (buzz) and blow a vibrating column of air through the instrument.

Trumpet: A relatively small brass instrument with three valves for changing pitch.
Trombone: Somewhat like an oblong trumpet, a trombone has but one moving part: a slide that controls the instrument's length, changing its pitch.
Tuba: A large, deep brass instrument with a massive bell and 3-6 valves.
French Horn: A devilishly difficult instrument to play, with three valves and a distinct, warm sound. In appearance, somewhat like a small, circular tuba.
Euphonium (Baritone Horn): Similar in a appearance to a medium-sized tuba.

Percussion: Most percussion instruments make noise when they are struck with another object, such as a stick. Other percussion instruments may be shaken or rubbed.

Mallets: Sticks with a round head attached.
Drum: An open cavity with a cylindrical frame and a membrane set tight over one end of the frame.
Bongos: Two drums of different sizes/pitches.
Gong: A flat, circular metal disc that is hit with a mallet.
Triangle: A triangular shape of metal, struck with a metal stick.
Shakers/maracas: Hollow objects with small, rattling material inside. Common in Latin music. Usually wooden or plastic.
Xylophone: A row of wooden bars of differing lengths. Played with mallets. Its appearances approximates that of a piano.
Marimba: A deep-toned xylophone with a smooth sound.

Ensemble: A group of musicians playing together, usually doing different things.
Chorus: An ensemble of singers.
Orchestra: An ensemble that can include any instruments, even singers.
Band: An ensemble that usually includes all the instruments except strings and singers.

Conducting: Using your hands (or a baton) to tell an ensemble how to play.
Cutoff: The main way a conductor tells the ensemble to stop.

Note: A single musical sound or pitch.
Tune: A sequence of notes.
Melody: The main tune in a piece of music.
Refrain: A structural piece of a song. A refrain is the main statement of a song and can be as short or as long as you like.
Verse: A structural piece of a song. A song often has many verses that share the same form but are all unique. Each verse sets up the refrain.

Tempo: The speed of the music.
Beat: The main rhythmic unit of a song.
Rhythm: A chain of sounds, arranged in a specific pattern. There are different genres of rhythms.
Dynamics: Dynamics are directions for how to perform a piece of music. This mainly includes tempo, volume, and tone quality.