Viola
Violas, slightly larger instruments than violins, put out a slightly deeper pitch and richer tone than the violin. As such, they’re perfect for playing rhythmic or harmonic accompaniments to the violins. They also frequently join the cellos and low strings in belting out the the melody or countermelody. Often referred to as the "middle child of the string instruments," the viola is actually one of the most unique instruments in the string section, with the capacity for emotion and great music making.
The violas play in a different clef than all other instruments (alto clef). Their uniquely warm and large sound coupled with their ability to move between the higher and lower sting sections, make the viola a very important member of the string orchestra.
Viola's come in varying sizes to fit the player, so be sure you are sized correctly!