Although the name "Sonatina" has no strict definition, it is generally applied to a piece that resembles a "Sonata" - but is smaller in stature. Sonatinas are usually shorter in length, lighter in character, and less technically demanding than the typical sonata.
Historically the term has been in use since at least the late baroque era. An early example being a one-page keyboard keyboard piece by G. F. Handel called "Sonatina". Although it is most often applied to keyboard works, a number of composers have written sonatinas for violin and piano (e.g. Sonatina in G major for Violin and Piano by Antonín Dvorák); and occasionally for other instruments, (e.g. the Clarinet Sonatina by Malcolm Arnold).