The definition of apraxia is difficulty getting your body to do what it needs to do in order to complete a task. A term also used is motor planning.
Praxis is when you think, I want to put my pants on, then your brain tells your muscles what steps they need to take in order to accomplish this task.
When you have apraxia, you have trouble figuring out what you need your muscles to do in order to accomplish the task.
The term can be used related to tasks, so you may hear someone talk about types of apraxia, such as speech apraxia, dressing apraxia, oral apraxia.