If you are taking the Trinity grade 1 music theory exam, you will need to be able to recognise or copy out an ostinato.
An ostinato is a short musical pattern which is used as an accompaniment, and is repeated over and over again, while the music around it changes. The words “riff” and “loop” have basically the same meaning, but “ostinato” is the word most often used when we talk about classical music.
Here is an example of an ostinato. It is in the left hand (bass clef) part of this piano piece. The pattern in bar 1 is repeated in bars 2, 3 and 4: