When someone makes a pledge, they make a serious promise that they will do something.

When someone pledges to do something, they promise in a serious way to do it. When they pledge something, they promise to give it.

If you pledge a sum of money to an organization or activity, you promise to pay that amount of money to it at a particular time or over a particular period.

If you pledge yourself to something, you commit yourself to following a particular course of action or to supporting a particular person, group, or idea.

If you pledge something such as a valuable possession or a sum of money, you leave it with someone as a guarantee that you will repay money that you have borrowed.