A Passion cantata is a cantata. The cantata takes its theme from the Passion of Jesus Christ, in other words his suffering until his death at the cross. Larger cantatas with this theme are known as oratorios.
Today, most of them are performed in the week before Easter.
In the English repertoire, the two classics are The Crucifixion (1887) by Sir John Stainer and Olivet to Calvary (1904) by John Henry Maunder. Other works include Sir Arthur Somervell's The Passion of Christ (1914), Charles Wood's St. Mark Passion (1921), Eric Thiman's "The Last Supper" (1930) and William Lloyd Webber's "The Saviour" (1942).
The most famous Passion cantatas are probably the two composed by Johann Sebastian Bach: the St John Passion (1724) and the St Matthew Passion (1727).
One notable work in Latin is Arvo Pärt's Passio Domini Nostri Jesu Christi secundum Joannem (The Passion of Our Lord Jesus Christ according to John) of 1982.