In angular material,If you want to display any unobtrusive alert on your GUI part to the users,then it provides Toast for designers. Toast is a term which is used to show alert in angular material and we use $mdToast service to display these toast.
See the example given below,there are two buttons one for simple Toast and other is Toast with action.
Simple Toast just display a message to the user and after few no. of miliseconds you want,it will hide. So we can define hide delay time as well. Secondly other is Toast with action that displays message and action as well. When you click on that action you can perform any activity via that.