A sequencer is a tool used to record, arrange, and play back musical events in a defined order. It allows notes, rhythms, and parameter changes to be programmed step by step or recorded in real time, creating structured patterns and loops. Sequencers are used to keep multiple instruments in sync, build evolving arrangements, and automate movement within a sound. For example, a sequencer might be used to create a repeating bass pattern while gradually changing filter or modulation values to add variation over time.