We very often use the words roligt and tråkigt in a very general sense. You very often hear Swedes say Det var roligt or Det var tråkigt meaning not much more than 'That is good/bad' (about the tense there, see here).
In other contexts though, if you're speaking about a movie for instance, rolig really means 'funny' and tråkig 'boring'.
"Rolig" can mean funny, amusing, or enjoyable. It really depends on context.
This is why ABBA says "money money money, must be funny", because the swedes just have one word for fun, funny and nice.
how precise are the swedes..! what is the difference between träffar/träffas and möter.....?
"Att träffas" means "to meet each other" so it could be either "Det var roligt att träffa dig" or "Det var roligt att träffas". "Att träffa" and "att möta" are synonyms, however, when you meet a person for the first time, you use "att träffa".
Can this sentence only be said when two people, knowing each other, meet and spend time together as planned? Or also when two stranger meet or get introduced to each other for the first time?
I would say that the second use is more common, because it might feel a bit formal. So when two strangers have been introduced, they certainly will say: "Det var roligt att träffas/att träffa dig" - if polite ! But of course, if two friends haven't seen each other for some time, and now has spent some time together again, the same phrase will be used when parting, (I see myself shaking hands here).
does "Det var roligt" really mens "It WAS nice" not "It IS nice". In swedish "var" is strongly used with emotional verbs and does not mean "it was...", but "it is...", isn't it?