What word is used to express the idea of unnecessary intrusion on someone else's affairs?

The term that best captures the idea of unnecessary intrusion on someone else's affairs is encroachment. Encroachment implies a gradual or stealthy intrusion into someone else's territory or space, whether it be physical, social, or metaphorical. It conveys the notion of a breach of boundaries, where one party oversteps their limits and infringes upon another's rights or privacy. This concept is particularly relevant in both legal contexts, such as property disputes, and social contexts, where personal boundaries are respected.

While intrusiveness is related, it typically refers more broadly to the act of intruding without necessarily suggesting a violation of territory. Similarly, encumbrance refers to a burden or hindrance, which does not inherently convey the idea of intrusion. Gossip, on the other hand, focuses on talking about others, especially in a negative or unwanted way, rather than on the act of unwarranted interference itself. Thus, encroachment precisely encapsulates the essence of unnecessary intrusion as it highlights the aspect of overstepping boundaries.