Synecdoche is a figure of speech in which a part of something is used to refer to the whole, or vice versa. The term comes from the Greek word "synekdoche," which means "simultaneous meaning".

For example, "all hands on deck" is a synecdoche because it uses the part "hands" to refer to the whole group of people on the ship. Similarly, "boots on the ground" is a synecdoche because it uses the part "boots" to refer to the whole soldier.

Synecdoche is often used in literature and poetry to create vivid, memorable images in a readers mind. For instance, in Toni Morrisons novel Beloved, the character Baby Suggs employs synecdoche in a sermon.

Synecdoche is also popular in advertising because it requires the audience to make associations and "fill in the gaps," engaging with the ad by thinking about the product. For example, the synecdoche "getting eyeballs" is used to describe catching the attention of an audience with advertising.

In addition to literature and advertising, synecdoche is common in spoken English, especially in reference to sports. It is also used in reference to political relations, including "having a footing," to mean a country or organization is in a position to act, or "the wrong hands," to describe opposing groups, usually in the context of military power.

Synecdoche is related to metonymy, which is another figure of speech that uses substitution to create more engaging writing. However, while both metonymy and synecdoche create a relationship in which one thing or idea stands in for another, the specifics of these relationships are different.