While working through 'Duet in D' for piano, by A. Diabelli, I came across this unfamiliar notation that looks like a slur between two notes of the same chord or some kind of bracket (see below). What is this notation called, and how do I read it?
It's an alternate way to notate an arpeggio.
arpège (Fr.), arpeggio (It.), arpeggi (It. plural): (Italian, meaning 'in the manner of a harp') a spread chord played from the top down or from the bottom up indicated by a vertical wavy line, a vertical square bracket or a curved bracket (the latter two signs are now uncommon).
(Direct quote from Dolmetsch. Always a great place to start when looking for music symbols)