Nulls are letters, numbers or symbols that represent nothing and are introduced to coded or enciphered letters as red herrings to confuse the codebreaker.

letters or words not connected to the plaintext message. These are used to confuse the cryptanalyst.

Meaningless letters used to confuse by modifying frequency distributions or predictability. Sometimes used to fill a message to a specific length.

In an antenna, near zero-level signals of sharp angular width seen in a radiation patterns. The opposite of lobes.