What does being tired all the time mean?

Variety of causes: This can be from lots of things. Sleep apnea, pregnancy, hypothyroid, poor diet or vitamin deficiency, diabetes, chronic fatigue syndrome. etc. Point is if this seems to be a persistent thing for you start by seeing your family doctor to get some things ruled out.

Could be many.: There are innumerable medical, nutritional and emotional conditions that include being tired as a symptom. These range from simple issues to those far more complex. A good checkup and blood testing would be a good starting point.