What is the difference between a Habit and a Task?

A task is something you need to do once. It has a defined outcome, and when it's done, it's done. "Order birthday present", "Call the accountant", "Finish the proposal" — these are tasks.
A habit is something you want to do regularly, where the benefit comes from repetition over time. "Do 20 minutes of yoga", "Review my project list", "Check my bank balance" — these aren't things you tick off once and forget. They're practices you want to build into your routine.
Putting habits on your task list causes two problems. First, they clutter your Today and Master lists with items that never truly go away. Second, a task list has no memory — it can't tell you whether you did something yesterday, or how many days in a row you've kept it up.
The Habit Tracker solves both problems. Keep your task lists for one-off actions. Use the Habit Tracker for the things you want to make part of who you are.