Transistor radios are small, portable devices that use transistors to amplify radio signals. They were first developed in the late 1940s and became popular in the 1950s and 1960s. These radios allowed people to listen to music and news on the go, revolutionizing how audio content was consumed. The invention of the transistor, a key component in these radios, made them more compact and energy-efficient compared to earlier vacuum tube radios. Transistor radios played a significant role in the rise of personal entertainment and are considered a precursor to modern portable audio devices like MP3 players and smartphones.