Definition - What does Tamas mean?
Tamas is a Sanskrit word meaning "darkness." According to yogic philosophy, tamas is also the name of one of the three gunas, meaning "quality" and referring to the basic qualities of nature. The other two gunas are rajas, meaning "passion," and sattva, meaning "purity."
The three gunas are always present in everyone. Regular practice of yoga and meditation can improve one's quality by balancing the three gunas as all three are essential to a certain degree.
Yogapedia explains Tamas
Each guna is associated with certain characteristics. Rajas is associated with energy; sattva promotes intelligence; and tamas is associated with the color black, night time, negative/dark energy and inactivity.
Those with tamas domination are lazy, dull, ignorant, inactive and greedy. They have psychological blockages. Owing to lack of self-care, their energies remain stagnant, causing poor health conditions. They are also easily and negatively influenced.