The word "aperture" refers to the opening or hole through which light enters a camera or telescope. It controls the amount of light that enters, affecting how bright or dim an image appears. Full definition
On the 5T however, this camera has the same focal length and wide aperture of the standard one. (tomsguide.com)
To explain further, a variable aperture lens allows a camera to mechanically adjust its lens opening to control how much light hits its sensor. (mobilesyrup.com)
Wide aperture on a camera especially helps to capture better shots in low - light settings. (businessinsider.my)