Which is correct: task or activity?
In this context, many terms are used for one and the same purpose. For example: operation, task, activity, etc. You can make it easy on yourself and say that it's all the same. But it is also possible to derive a structure, which is quite OK.
An example: There are several phases in the project. For example, preparation, implementation and completion. Each phase contains different work packages. Depending on the size of the project and the individual style of the project manager, these work packages can be further broken down into individual tasks. This brings us to the tasks and activities.