These are the people who do just enough to get by. They lack regard for deadlines, have very little motivation, and put minimal effort into their work.
The worst part is, working with a lazy colleague can make your life more difficult, especially if you're teamed up with this person on a project or work directly with them on a regular basis.
Invite this person out to lunch and ask if they truly enjoy their job. Try to get to the bottom of things.
Without insulting him or her, mention that you've noticed a lack of enthusiasm. Explain how them not meeting deadlines or completing all their tasks affects you and others in the office.
If nothing changes, talk to their manager.