Which word means to get involved in a situation that is not your concern?

The term that best fits the definition of getting involved in a situation that is not your concern is "interfere." This word carries a connotation of inserting oneself into a matter without invitation or necessity, often leading to unwelcome or disruptive consequences. For instance, if someone were to interfere in a personal dispute between two friends, they may cause more issues rather than help.

In contrast, "intervene" typically implies stepping in to assist or stop something that is harmful. It is generally viewed in a more positive light, as one intervenes to provide help in a situation, usually with the best of intentions.

"Mediate" involves acting as a neutral party to facilitate discussion and resolution between two or more parties, suggesting a structured effort to aid in resolving conflicts rather than simply butting in.

"Negotiate" refers to the process of discussing terms to reach an agreement. This word applies to bargaining situations and does not inherently involve imposing oneself on a situation outside of one’s own concerns.

Thus, while all these words relate to engaging in situations involving others, "interfere" specifically captures the idea of involvement that is unwelcome or outside one's business.