The play or discard of a card is called a safe action if it is promised to progress the game in a helpful way. On the other hand, an action is unsafe if taking it may discard or bomb a card could lose the game. Usually, the notion of a safe action takes into account the discard or bomb of important cards, and not whether the action may lose the game due to endgame considerations. The idea of a safe action is subjective, dependent on how careful your system (and team playing) can afford and attempt to be.
Some actions count as safe across essentially all systems:
Others count as safe only only for some systems:
Many systems, including Sieve, Referential Sieve, Reactor, and Turbo play with a safe action principle. These systems heavily orient their clues around being able to provide a safe action whenever one exists without having to mean anything extra with the clue. Usually, this means adopting a fill-in clue convention: any time an established card is touched, fully-revealing it to be playable or trash, the immediate conventional meaning of the clue is to play or discard the card, and not to play or discard anything else.