The idiom "bury one’s head in the sand" means to ignore or avoid a problem or an unpleasant situation, hoping it will go away on its own. It comes from the image of an ostrich burying its head in the sand to avoid danger, even though it's a myth that ostriches do this.
People use this idiom when someone is avoiding a problem or a situation that they should be dealing with. For example, if someone is having financial problems but refuses to acknowledge them, they are burying their head in the sand. Or, if someone is aware of a serious health issue but does not want to get it checked out, they are also burying their head in the sand.
In other words, it means to ignore the problem instead of facing it head-on. It's not a good way to deal with problems because they usually don't go away on their own and can become worse over time.
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