Catchword, byword, shibboleth, slogan mean a phrase that catches the eye or the ear and is repeated so often that it becomes a formula.
Catchword usually applies to a phrase that serves as the formula or identification mark of an emotionally charged subject (as a school of thought, a political party, or a cause) and that is often used by those who have only a superficial knowledge of the subject and its philosophy and basic tenets.
Byword sometimes denotes a significant phrase that is repeated far and wide until it has become a proverb. The more usual sense is a person or thing that has become proverbial as the type of certain evil, ludicrous, or shameful characteristics and whose name, therefore, has become the object of concentrated scorn or contempt.
Shibboleth was the word which, in Judges 12, the Ephraimites fleeing from the Gileadites could not correctly pronounce when tested, thus giving away their identity to Jephthah as his enemies; it typically applies to a fixed usage (as a word, phrase, or speech sound) whose employment identifies a person as belonging to a particular party, class, profession, ethnic group, or time. The term basically stresses help in placing a person, but may also imply the emptiness and triteness of such usage and then approach platitude in meaning.
Slogan, originally a cry used in battle, has come to mean a phrase that is a shibboleth of the party or group using it. It may be a phrase deliberately invented for the sake of attracting attention to a party or group or it may be an eyecatching or ear-catching bit used as an advertising device.