It's a naming convention for your microflows, so you know what microflow is used where.
IVK --> Invoke
DS --> Data Source, mostly used on grids / views populated by a microflow
ACo --> After Commit, microflow which is run after commiting an object, used as an event handler on an entity.
IVK = Invoke and is usually used to indicate that it is a button microflow.
DS = Data Source and is usually used to indicate that this microflow is a datasource for a grid or dataview.
ACo = After Commit and identifies that this microflow is used on an entity after commit event.