Setting.  The last of The Big 5 (story essentials) and more than just the location for your story.  Setting is used to provide not only a physical backdrop but an emotional landscape as well—two critical elements that impact your characters (to whatever degree you choose) from start to finish.  Physical settings are a no brainer.  It's the emotional setting I want to discuss here.  They help elicit a deeper response from the reader by way of sensory information we process every minute of the day.  Take for example the deafening scream of an air raid siren in the still of the night.  That sets a great scene and makes a pretty good opening segment too.  How about smells?  The acrid smell of smoke emanating from the basement or the unmistakable odor of a skunk beneath the screen porch.  It's all good stuff because it can initiate immediate action, dialogue, emotion and conflict.  What about physical sensations?  Describing the goosebumps on your character's arms when she sees a strange shape move past the window in the dark of the night.  Yup, works for me. 

Simply put, when creating the setting(s) for a story, the writer's palette should include more than just what a character sees.  Beyond the basic geography, some writers include specific background information like day, date, time, weather conditions, and so on.  As mentioned before, however, don't get too wordy or you slow the story down and bore your reader with tiresome (i.e. unimportant) details.