Cavaletti are very low jumps, often (but not always) made all of one piece, with a wooden rail nailed to cross pieces. They generally are no more than a foot high.
Cavaletti are used to encourage elevation of gait in dressage horses, to teach young horses to pick their feet up better, and in early jump training (of both horse and rider).
The pole is off set so that the caveletto (cavaletto is the correct singular but seldom used in English) can be adjusted between different heights, although this one is broken. (Image source: 4028mdk09 via Wikimedia Commons).