Amplifiers come in a variety of designs and can look like in-ear or behind-ear hearing aids.
However, they are not programmed to a hearing test. Instead, they amplify all frequencies to make everything louder (but not necessarily clearer).
BTE hearing aids sit behind the ear and look similar to a RIC model with some key differences.
They have tube that connects the body to the dome, rather than a wire and all of the tech is on the outside, so they tend to be larger than RICs.
RIC hearing aids sit behind the ear and look similar to BTE models.
Unlike a BTE, a wire connects the hearing aid body to the dome and a tiny receiver goes inside the ear so this type is typically the smallest.