To make things more confusing, each of those six dinim have alternate meanings that people use at least as often as the ones given here. This leads to many misunderstandings and lots of pointless flamewars.
1) M’ikar hadin: The original chiyuv d’oraisa before any takanos were instituted, e.g. forbidding gerushin bal korcha, tzava’ah, karmilis and most of a woman’s rights under the kesuba are d’rabanan.
2) Chumra: Any shita more stringent than the most lenient opinion the speaker knows
3) Kula: Any shita more lenient than the most stringent the speaker knows
(both terms are used this way only to put others down and using the words this way is probably ona’as d’varim)
4) Hanhaga: Something with no halachic basis that people do for personal reasons like saying certain prakim of tehillim or trying to be yotze kol ha’deios on one particular mitzva that they have a cheshek for
5) Minhag: Things that rishonim bring down as minhag yisrael like saying baruch she’amar (RaMBaM hilchos tefilla)
6) amaratzus: People who follow an opinion the speaker never heard of/dislikes.
Hope this list helped. 😉