ELI5: Explain Like I'm 5

Low-noise block downconverter

A low-noise block downconverter (or LNB) is a device used in satellite TV and radio systems. It helps convert high-frequency signals from satellites into lower frequencies so they can be received by the receiver inside your satellite TV box. The LNB reduces the amount of noise from the signal so you can get the best picture and sound quality when watching TV.