Anything that's supernatural, for example gods and Easter Bunnies, are impossible.

Wikipedia - Deity

A deity is a supernatural being considered divine or sacred. The Oxford Dictionary of English defines deity as "a god or goddess (in a polytheistic religion)", or anything revered as divine. C. Scott Littleton defines a deity as "a being with powers greater than those of ordinary humans, but who interacts with humans, positively or negatively, in ways that carry humans to new levels of consciousness, beyond the grounded preoccupations of ordinary life". In the English language, a male deity is referred to as a god, while a female deity is referred to as a goddess.

Religions can be categorized by how many deities they worship. Monotheistic religions accept only one deity (predominantly referred to as God), polytheistic religions accept multiple deities. Henotheistic religions accept one supreme deity without denying other deities, considering them as aspects of the same divine principle; and nontheistic religions deny any supreme eternal creator deity but accept a pantheon of deities which live, die and may be reborn like any other being.

Although most monotheistic religions traditionally envision their God as omnipotent, omnipresent, omniscient, omnibenevolent, and eternal, none of these qualities are essential to the definition of a "deity" and various cultures conceptualized their deities differently. Monotheistic religions typically refer to God in masculine terms, while other religions refer to their deities in a variety of ways – masculine, feminine, androgynous and without gender.

Historically, many ancient cultures – including the ancient Mesopotamians, Egyptians, Greeks, Romans, and Norsemen– personified natural phenomena, variously as either deliberate causes or effects. Some Avestan and Vedic deities were viewed as ethical concepts. In Indian religions, deities were envisioned as manifesting within the temple of every living being's body, as sensory organs and mind. Deities were envisioned as a form of existence (Saṃsāra) after rebirth, for human beings who gain merit through an ethical life, where they become guardian deities and live blissfully in heaven, but are also subject to death when their merit is lost.