A shadow is a dark shape that is formed when an object blocks a source of light. On a sunny day, practically everything casts a shadow — including you. Shadow can also act as an action, like when you shadow, or follow, someone on the first day at a new job.
Depending on its use, shadow can have negative or positive connotations. Children often play with their shadows and think of their shadows as constant companions, like in the song lyric "just me and my shadow." On the other hand, you could be such a wimp that you fear your own shadow or at least fear what lurks in the shadows. Used as a verb, a spy could shadow you without your knowledge. Or, your faithful dog might shadow you as you pace around the house. You might be sick and tired of living in the shadow of your older sister who always seems to be the center of attention — blocking you from the spotlight.