Savannahs are a domestic breed of cat with some degree of the African Serval heritage.  The goal of the breed is to resemble a serval in appearance:

Body: long, lean, tall, and graceful with long neck and legs (back legs slightly longer than front legs)

Head: small in proportion to the body, shaped like an equilateral triangle

Eyes: slightly hooded brow, almond shaped; eye color varies

Ears: very large, wide at the base with rounded tips, placed close together on the top of the head and faced forward, dark colored with pale band across the center (called ocelli or night-eyes)

Coat: short to medium length, may be slightly coarse in texture, lays relatively flat but still full and luxurious in thickness

Tail: medium in length and thickness of fur (not thin and whippy), banded in color

Pattern: the standard pattern is dark-brown to black spotted tabby; nonstandard patterns include stripped or marbled tabby

Colors: standard colors include solid black, or spotted with a background of black, smoke, silver, brown, or gold. Nonstandard colors include white (snow), blue, orange, torbie (multicolor patched with orange).

Size: ranges from 8-20 lbs. Most savannahs are between 10-15 lbs. Although it is often claimed that savannahs are the ‘largest breed of domestic cat’, there is no guarantee that a given individual will attain a very large size. Because they are so tall and long, savannahs usually look much larger than other breeds of cats at the same body weight. Some individuals do get to be 20+ lbs, and it is usually (but not always) the males of higher percentage generations (F1-F3). Males are usually larger than females, especially neutered males.  F2, F3 and later generation females are usually average cat size (10-12 lbs).