What is one similarity and one difference between infrasound and ultrasound?

The generic word 'sound' includes the words 'ultrasound' and 'infrasound'.

The distinction between 'sound' - as in what we can hear - and the other two is a bit arbitrary. 'Ultrasound' refers to sounds that have frequencies above the top limit of our hearing; 'infrasound' refers to sounds that have frequencies below our lower limit of hearing.

From the Greek: 'ultra' = above; 'infra' = below.