Triguna or three gunas are the three main qualities of mind. They are Sattwa, Rajas and Tamas or good, indifferent and bad respectively.
The mental powers exist parallel to tridoshas that control the body.
Sattwa means purity. Persons of this quality are calm, kind and thoughtful. This is the best mental quality to posses.
Rajas roughly translates into activity.
This kind of persons will be very active and seek incessant activities.
Tamas is darkness.
The most unfavorable mental condition, the persons in this condition have a lethargic mind.
There is Sattwa, Rajas and Tamas (all the trigunas) in every individuals. The dominance of a guna in that person tells about the character of that person. It is said that there is no one man on earth without at least a bit of purity in his mind.