What is the meaning of Flattie?

Alternative form of flatty

A flattie spider, generally in the family Selenopidae, so called because of its flattened, sprawling shape.

A flat white (type of coffee).

A flat marinated cut of meat.

A flat store.

A flat-bottomed sloop-rigged sharpie.

A traditional two-dimensional motion picture, as opposed to a deepie.

A flat earther.

The operator of a flat joint, or crooked gambling operation.

A Flat-coated Retriever.

A person with a flat chest, i.e., without breasts.

A navel that is neither protruding nor sunken.

A flatmate.

Source: wiktionary.org