What does -e and -ne means in bash script?

#!/bin/sh
# https://stackoverflow.com/questions/34077070/what-does-e-and-ne-means-in-bash-script
# just in case bash isn't available, this runs fine with sh

#user variables should always be lowercase
expected_args=1
e_badargs=1

#it's good practice to quote all variables, even if you know they're numbers
if [ "$#" -ne "$expected_args" ]; then
  echo "Usage: $(basename $0) {arg}"
  exit "$e_badargs"
fi

#check if this is a directory, not just that it exists
if [ ! -d "$1" ]; then
  echo "$1 does not exist or is not a directory"
  exit "$e_badargs"
fi

#quote this, in case there's a space in the directory name
for myfile in "$1"/*; do
  #also quote $myfile in case of spaces in the file name
  if [ -d "$myfile" ]; then
    echo "$myfile (DIR)"
  elif [ -f "$myfile" ]; then
    echo "$myfile"
  fi
done