We are told according to the Britannica article referenced below that the triangle is a percussion musical instrument which is in its name shape and made of steel, a rod bent into the triangle shape with a little gap at the one end.
It has a loop attached which consists of gut or nylon.
A single stroke on the triangle make a clear sound definitely heard in the orchestra.
It is usually used sparingly in well placed notes by the composer and this is very effective as part of the performance.
It played a key role in Franz Liszt’s Piano Concerto No 1 in E Flat Major and has been referred to as a Triangle Concerto.
It is a very tiny and portable part of the orchestra instruments to own and one of the more inexpensive ones.