Management by objectives is a way to make sure a company meets its goals. It involves setting powerful goals and objectives, and then making sure everyone in the company is working together to achieve them.
For example, a company might want to make more profits this year. The management sets an objective to increase profits by 10%, and then everyone in the company- from the CEO to the customer service workers - works together to try to make that goal happen. They might create a plan on how to increase profits, or decide to focus on customer satisfaction, or find ways to reduce costs. At the end of the year, the company can measure if it achieved its goal or not. That way, everyone in the company is working together to reach the same goal.