LON-CAPA demonstration resource. Some of the information for this resource quotes from and summarizes content in
Principles of Violin Playing by Ivan Galamian. Second Edition (1985) Prentice-Hall, Inc. New Jersey

Oak Spring Studios

Left Hand

The left hand serves two purposes:

fingering of notes
vibrato

The categories of fingerings and vibratoes can work to generate highly complex sound. Careful attention must given to the proper form of the left hand. While quick actions, glissandos, harmonics, trills, shifts, and double stops add great embellishment, improper execution can lead to a mediocre sound.

Here is a brief glossary of left hand activities:

double stops: two fingers are creating separate intonations on two different strings
glissando: the quick ascension or descension of notes
trills: quick oscillatory actions by a left finger
harmonics: reduced pressure by intonating fingers to allow for alternative pitches due to adjusted string vibrations
shifts: movement of the left hand in toto relative to the violin scroll