(informal, chiefly in the negative) To be new, naive, innocent, inexperienced, or easily deceived.

The quality or state of being seropositive, of having blood serum that tests positive for a given pathogen, especially HIV. / Seropositivity rate, seroprevalence.

(figuratively, idiomatic) When the pressure is on; when the situation is critical or urgent; when the time has come for action, even if it is difficult.

Pertaining to life; vital.