Opinion - a view or judgement formed about something, not necessarily based on fact or knowledge.
Rumour - a currently circulating story or report of uncertain or doubtful truth.
Humans talk, don't they? You're walking through a school hallway, going to the next classroom and you hear something you wish you didn't. Someone commenting on your hairstyle, or the funny way you walk - or maybe something they have heard. About you, of course. Who else could it be about? Apparently she said that you said that he has weird clothing. Or that you slept with her ex boyfriend and you just can't do that, right?
Rumours. Opinions. Apparently. Apparent lies. These are all little mutations of the human nature that create fire within society. Things that were never meant to be said, but you only told your best friend because it's only one person, right? Well this is how it goes. We as humans thrive off knowledge, gossip, knowing what is going on - even if it means that someone's rep is in jeopardy or someone could go to jail for doing something wrong, we have to know what is going on.
It's just human nature, to learn little tidbits of information that others don't want us to know. But dealing with rumours is a different story.
Firstly think about who is spreading the rumour. If you know it isn't true, then there is no point bringing it up into conversation if people aren't talking about this. I have seen this many times before, and basically if you want the rumour to go away think of it as a fungus on your toe... you aren't exactly going to discuss that with people, now are you?
When people say bad things about you, it is normally because they are jealous or are below you. As Taylor Swift taught me, people throw rocks at things that shine. Remember this, people will support you, but they don't want you being better at things than them. Rumours start because people either want to bring you down, or haven't realised what they are doing is hurting you.
Rumours aren't always from the source, as they get around they become more and more fabricated, and when they get back to you - it's almost like they were never to do with you in the first place, but people added bits and bits to the conversation to either wreck your reputation, or because it's a tricky game of chinese whispers, fun.
Don't believe everything you hear, the less you talk about the rumours, then they will die down. You are above the people wanting to bring you down.