What is the difference between a sequencer and an arp?

Excuse me, could you please elaborate on the distinction between a sequencer and an arp? I'm particularly interested in understanding how they differ in terms of their functionality, purpose, and the musical effects they produce. As a musician and producer, I often find myself using both tools in my music creation process, but I'm still not entirely clear on the nuances that set them apart. Could you provide a concise yet comprehensive explanation to help me better grasp the concept?