ABC means Activity Based Coasting while ABM means Activity-Based Management. These are known to be tools that can be used to manage various business activities. ABM just focuses on business processes. ABC is effective in the costing process because it will be in charge of providing the various expenses that are needed, like the rent, supplies, and so much more.
ABM will be more focused on getting to know the various activities that can be effective in managing various activities that are meant to improve the organization. ABC is also focused on improving the value of the activities that would need to be given in order to make the customers happy.