Task here is a synonym for activity in Project Management, or individual day to day work.
Excerpt from Wiki:
In project management, a task is an activity that needs to be accomplished within a defined period of time or by a deadline. A task can be broken down into assignments which should also have a defined start and end date or a deadline for completion. One or more assignments on a task puts the task under execution. Completion of all assignments on a specific task normally renders the task completed. Tasks can be linked together to create dependencies.