What do you think it means? To me it appears as though the player has the option of a critical; as in "do I want to do a critical hit?".
The demo shows the player pulls up VATS on a deathclaw, and the menu title is 'Crit__________________", and the options include select, and accept.
Imediately afterwards, the screen appears to show the option to press X to 'execute critical', or press B to abort.
**Edit: mobile browsers might only show the 1st frame of the animated gif.