While "slimline" is not a defined term, slimline seats have less padding in the back. Seat pitch and width in economy class have also been decreasing, In 1985 none of the main four US carriers offered a seat less than 19 inches wide. Since the beginning of the 21st Century until 2018 average seat width decreased from 18.5 to 17 inches, and sometimes as low as 16.1 inches.[3]