The term 'negating prefix' refers to a type of word that is added to the beginning of another word to change its meaning. The most common example of this is the prefix 'non-', which is used to indicate the opposite of the word it is attached to. For example, adding 'non-' to the word 'ACTIVE' would create the word 'non-ACTIVE', which means not ACTIVE. This prefix is often used to create words with negative connotations, such as 'non-essential' or 'non-negotiable'.