In the Bhagavad Gita's seventeenth chapter the threefold guna classification extends to food, and tamasic food is described as stale, tasteless, putrid or left over, favoured, the text says, by those given to dullness and inertia. The same grid marks giving made without respect, at the wrong time or place, or to an unworthy recipient as tamasic, and an action undertaken from delusion, without regard for consequence, as tamasic in character, extending the guna into an ethical as well as a dietary vocabulary.
Tamas is not simply condemned as evil in this scheme; rest, sleep and the stillness that allows recovery are tamasic in nature and necessary in their season, and the classical view holds that no person or substance is purely tamasic, since all three gunas are always present together in shifting proportion. Spiritual practice generally aims to lessen tamas relative to sattva and rajas, treating excessive inertia, confusion and negligence as the obstacle most in need of reduction on the way toward the transcendence of all three gunas together, called gunatita.
Popular use sometimes treats tamas as a simple synonym for laziness, losing the doctrine's more exact claim that tamas is one necessary strand among three, present in everyone, rather than a flaw confined to some people and absent in others.