Discussion and debate are neutral terms, implying a (not necessarily heated or combative) exchange of views. Dispute and argument aren't neutral - they imply an exchange of views that got heated and/or combative, and led to raised tempers (e.g. raised tension, raised voices or even physical aggression). It is possible to have a discussion and for both parties to be broadly in agreement (e.g. Julia and I had an interesting discussion about the importance of learning a foreign language. We both thought exactly the same way...." A debate implies that parties took different views, but didn't necessarily get heated on the subject. (e.g. there was an interesting debate on TV last night about the Middle East....) Argument implies opposing views and raised tempers...."I had an argument with my boyfriend last night and we said some things to each other that were probably best left unsaid..." Dispute also implies opposing views. 'I had a dispute last night with the neighbours about their noisy parties. Things got quite nasty..."

The words have overlapping meanings. To me "discussion" just means talk about one central topic. It can be completely friendly. "The ten of us had a discussion about where to go for dinner." It could be a "spirited discussion," meaning people expressed strong points of view. For example, "a spirited discussion about which is better, Windows or Macintosh." It could be a "heated discussion," meaning, yes, it got angry. If I know that the discussion is about a controversial topic, such as climate change, I might wonder whether it stayed friendly. As a sort of JOKE, one could refer to a loud fight as a "spirited discussion." I don't agree that an argument is ALWAYS angry. The essence of the word "argument" is "going in circles" so it means a long discussion on a single theme that goes around and around and comes at it from different angles. But usually the word implies some degree of heat.

To discuss is defined as 1. "To speak with others about something / to talk something over OR 2. To examine (a subject) in speech or writing" An argument is defined as 1. "A discussion of differing points of view; 2. A quarrel; a dispute 3. a. A course of reasoning aimed at demonstrating truth of falsehood b. A persuasive reason" I, personally, like discussions much more than arguments because I'm open to listen to others opinions and can also benefit from other ideas.

It was probably neither an argument or a debate - a discussion is simply an exchange of views, and can be quiet relaxed and friendly. An argument is a verbal 'fight', involving strong opposing views and some degree of anger. It often involves shouting. A debate is more formal and organised. You might have a debate on TV, in which politicians are invited to give their views. There will be a chairperson, and often a vote at the end.