A "stylus slot" refers to a small space or compartment designed to hold a stylus, which is a pen-like tool used to interact with touchscreens or electronic devices. Full definition
Further, both the tablets support stylus pen input with a neat stylus slot built along the side allow for safe storage of the stylus as well. (goodereader.com)
The Epic's cloth - tipped stylus slots into its left side and is tethered to the tablet's bottom edge by a short cord. (laptopmag.com)
It's essentially a thinner, narrower version of the Note 8 without any S Pen Stylus slot to worry about; it's bezel width and overall girth have received a notable cleaving. (cnet.com)