From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): (n.) The small olive-shaped berry of the European and Oriental caper, said to be used in pickles and as a condiment.

(2): (n.) The currantlike fruit of the African and Arabian caper (Capparis sodado).

Holman Bible Dictionary [2]

capparis spinosa  Ecclesiastes 12:5

International Standard Bible Encyclopedia [3]

kā´pẽr - ber - i ( אביּונה , 'ăbhı̄yōnāh  ; κάππαρις , kápparis  ;  Ecclesiastes 12:5 the Revised Version, margin): The translation "the caperberry shall fail" (the Revised Version (British and American) "burst") instead of "desire shall fail" (the King James Version) has the support of the Septuagint and of some Talmudic writers (see G. F. Moore, JBL , X, 55-64), but it is doubtful.

The caperberry is the fruit of the thorny caper, Capparis spinosa (Natural Order Capparidaceae ), a common Palestine plant with pretty white flowers and brightly colored stamens. Largely on account of its habit of growing out of crevasses in old walls it has been identified by some with the Hyssop (which see). The familiar "capers" of commerce are the young buds, but the berries were the parts most used in ancient times; their repute as excitants of sexual desire is ancient and widespread. Various parts of this plant are still used for medical purposes by the modern peasants of Palestine.