They were the first congregation in the Church of regular clerics or canons regular (_clerici regulares_ or _canonici regulares_).

On account of the early renown for piety which they acquired, it became usual to style any devout person a Theatino or Chietino.

They were also sometimes called Tolentines, from the name of their principal church dedicated to St.Nicholas of Tolentine.

Their dress being similar to that of the Jesuits, they were through ignorance often mistaken for them.

The term was also applied to some of the Jesuits who had been in Florida and afterward went to Manila; to the Jesuit missionaries in Japan; and to the first Jesuits in the Philippines.