A bequest is a gift that you make through a will or a revocable trust functioning as a will. A beneficiary designation is a gift you make  by way of a contract. Life insurance policies, bank accounts,  brokerage accounts, and retirement plans are examples of assets that pass by contractual beneficiary designations.
If you don’t name a beneficiary for one of these contracts, or if the beneficiary designation is to someone who has predeceased you or from whom you have since been divorced, then the assets will go to your probate estate and pass by bequest.  Though probate isn’t  as bad as it is sometimes said to be, it can add costs and  delay to estate administration. Most people don’t like that so it’s important to complete and to regularly review your beneficiary designation forms.
You can make a gift to charity via bequest or beneficiary designation form.