What is Critical ?
Critical is (adj) 1. dangerous and difficult With the enemy attacking on all sides, our position was becoming critical. 2. extremely important He made a critical decision to break off the negotiations. Critical relief supplies have been held up at customs. 3. very serious The pilot of the crashed plane was in a critical condition last night. The hospital said that her condition was critical. 4. which criticises The report was highly critical of the minister.
source: Easier English, Student Dictionary Upper Intermediate Level