What is the meaning to 'bury your head in the sand?

It means to ignore something, even when that something could be dangerous to the person in question or to those on whom he/she bears responsibility.

The imagery comes from the (erroneous) belief that ostriches bury their heads in the sand. The idea is that, with one's head under the ground not able to see or hear outside, they aren't aware of what's going on: usually at a time when they SHOULD be aware.

The phrase can be used more forcefully to imply that this ignorance is intentional and that the object of the idiom is making a very poor response to a crisis.