OutSystems Platform allows modelling business processes. These business processes are flows of work and information that evolve through several stages from the moment they are created until they end. At each stage, some work is performed by (typically) a different person or even automatically by the server.
To understand this better, you may want to read about business process modelling (or BPM) to gain background knowledge about this topic. You can read this Wikipedia page or see some visual examples of business process workflows.