Installation Art

So What exactly is installation art? I asked myself this question right away.  What it is, is an artistic genre of site-specific, three-dimensional works designed to transform the perception of a space.  For example in class we looked at Rachel Whitread's 'Embankment' which is a room full of large white boxes shaped into different structures.  The picture below shows exactly what I mean.

When I searched through installation art after class, I came upon the pictures shown below. The First one is basically a room full of junk.  Although it does take up space in a room, I feel as though this really isn't art.  Because if it was, then wouldn't hoarding be considered a form of installation art? And i truly don't believe that hoarding is any form of art.  The second picture below is a falling garden done by a Swiss artist named Elizabeth Schuppe.  This installation art is very interesting to me.  I feel like because it is so unusual to see a garden hanging from the ceiling it really catches peoples attention.  And because it takes up a three-dimensional space, it can definitely be considered installation art.