My tasks are blocked: what does it mean?

In Casual, you get to develop project's workflow within which you create dependencies between tasks. If a task depends on the one that is not completed yet, it will be blocked.

The blocked task feature helps you focus on the current tasks leaving the distractions such as other tasks aside. 

• On the canvas, the gray tasks are the blocked tasks. 
• In Overview window, blocked tasks have a lock icon on them.

You can unlock a task only by completing the one on which it depends.