Answer:
A Concerto is a musical composition in which a soloist is accompanied by and orchestra. When we talk about a Classical concerto, we refer to the Concertos composed between 1750 and 1830 (XVIII and early XIX Centuries). The main structure of Classical concerto is the standart cycle of three movements. The first and the last movements are predictable in general: as an opening, we can notice a Sonata way of composition, and in the finales, the main form are rondo and sonata-rondo. In between the first and the last movements, we can find a less predictable structure with A B A design, sometimes a kind of dialogue or free variations. The most common Concertos by instrument are for the violin, the cello and the piano. In the Classical era, flute and trumpet concertos where introduced.
In general, the most common genres for Concertos by style are: Concerto Grosso (Barroque era); Ripieno Concerto (Barroque era); Solo Concerto (Barroque and Classical era), and Concertino (late XIX and XX Century).
Explanation:
As I already mentioned, a Concerto is a musical composition in which a soloist is accompanied by and orchestra. The soloist and the orchestra are related by alternation, competition and combination. The word "Concerto" had changed all along the Music History, that's the reason why we can find Barroque, Classical and Romantic styles for this kind of composition. It is generally composed of three contrasting movements (fast-slow-fast) that are usually based on certain designs such as sonata form, A B A (musical sections), varations and rondo (A B A C A). Anyway, we can find concertos with 4 movements and even some others without a solo.
The 4 main styles of Concertos are:
<em>1. Concerto Grosso:</em>
"Grosso" means "big", so it is a "big concerto" in which a small group of soloists is accompanied by an orchestra. The melody in this kind of concerto is passed between soloists and orchestra all the time. It is a concerto from the Barroque era, that started in Italy and went to Germany, giving inspiration to Vivaldi, Handel and Bach.
<em>2. Ripieno Concerto:</em>
This concerto refers to a work for an ensemble, so the solo is weaker or nonexistent, and it could be a sonata or a symphonia type. In both types of concerto, there is contrast in between movements: slow-fast-slow-fast (sonata); fast-slow-fast (symphonia). This style belongs to Barroque concertos compositions as well as the Concerto Grosso.
<em> </em><em>3. Solo Concerto</em>
The soloist, accompanied by the orchestra, shows its techniques, all along the three movements. Especially, In the second movement, the soloist tend to show deep emotions. This kind of Concerto was exclusively witten for violins until early 18th Century, when other instruments appeared (early 18th Century). and this is the typical Classical Concerto.
<em>4. Concertino:</em>
A concertino is a "little concerto" in one movement, shorter and freer in comparison to a solo concerto. It is played without and orchestra or just with a few instruments accompanying. This style of Concerto was created in the XIX Century and it could be composed for multiple instruments like clarinet, bassoon, harp, percussion, oboe, horns etc.