What is Baronet?

Legal Definition
A baronet (/ˈbærənɪt/ or /ˈbærəˌnɛt/; abbreviated Bart or Bt) or the rare female equivalent, a baronetess (/ˈbærənɪtɪs/, /ˈbærənɪtɛs/, or /ˌbærəˈnɛtɛs/; abbreviation "Btss"), is the holder of a baronetcy, a hereditary title awarded by the British Crown. The practice of awarding baronetcies was originally introduced in England in the 14th century and was used by James I of England in 1611 as a means of raising funds.

A baronetcy is the only British hereditary honour that is not a peerage, with the exception of the Anglo-Irish Black Knight, White Knight and Green Knight (of which only The Green Knight is extant). A baronet is addressed as "Sir" (just as is a knight) or "Dame" in the case of a baronetess but ranks above all knighthoods and damehoods in the Order of precedence, except for the Order of the Garter and the Order of the Thistle (and the dormant Order of St Patrick).

Baronets are not deemed members of the nobility, but rather, titled gentry. Their social rank is roughly equivalent to the petty nobility in some countries of continental Europe.
-- Wikipedia
Legal Definition
An English name or title of dignity, (but not a title of nobllity,) established A. D. 1611 by James I. It is created by letters patent, and descends to the male heir. Spelman.
-- Black's Law Dictionary
Legal Definition
An English title which is a dignity of inheritance, created by letters patent. See 1 Bl. Comm. 403.
-- Ballentine's Law Dictionary