Among experts, "big cats" refers to those animals of the genus Panthera, where a genus is a group or category of organisms of similar characteristics that can contain one or more species.
Below, you will find the main characteristics and differences between the animals people usually consider as the main big cats: lions, tigers, jaguars, leopards, panthers, pumas, lynx and cheetahs.

I hope you find this useful and that it helps you spot the difference easily from now on!
Tiger
The tiger is the largest cat species, with several subspecies including the Bengal and Siberian. The sizes of tigers varies greatly between different populations.

Tigers are most recognisable by their vertical black stripes on a background of orange. The stripe pattern is actually on the skin of the animal, and it is unique to each tiger (much like fingerprints on humans).

Tigers are able to swim well, along with jaguars. They also generally hunt alone.

Tigers can live to around 25 years old, both in the wild or in captivity. Tigers in the wild can be found in many different locations — though they are mainly spread across Southeast Asia, China, and India.[img][/img]
Lion
Lions are the second largest big cat, after the tiger. They don't have any discerning skin/fur patterns, although the male adult lions do have a signature, recognisable mane of fur around their face.

Female lions do most of the hunting, often at night. However, only 1 in 5 hunts end in a kill. Therefore scavenging for food (in other words, stealing from other predators) is also vital. They mainly prey on wildebeest, zebra, and gazelle, though they will attack other animals too, including buffalo and hippos. Lions are the only big cats to hunt cooperatively, working together to find food.

In the wild, lions live for about 14 years, and in captivity they can live up to several years longer. Lions are found in Asia and in sub-Saharan Africa.[img][/img]
Leopard
The leopard is the smallest of the four big cats, among the tigers, lions, and jaguars. Leopards are found mainly in sub-Saharan Africa, but they also exist in South Asia (India, China, Malaysia, and Indonesia).

Leopards have a comparatively long body and short legs, with a large skull and powerful jaw. They look similar to the jaguar, however they are smaller and lighter and the fur patterning is slightly different. On a leopard, the rosettes (circular markings on their fur/skin) are smaller and more closely spaced together, and don't usually have black spots in the centre of the rosettes like jaguars do. The leopard's rosette pattern and overall colour can vary slightly, however, depending on where they live.

Leopards are very adaptable, they can exist in a range of different habitats, they can hunt and eat many different animals, run very fast, are very stealthy hunters, and are excellent tree climbers.[img][/img]

Jaguar
The jaguar is the only big cat in the Panthera genus that can be found living in the Americas. The jaguar is the third largest cat (after tigers and lions) and they can be found in southern United States, Mexico, most of Central America, and across the north of South America.

The jaguar is often confused with the leopard due to the markings on the coat. Jaguars are, however, heavier, larger, and sturdier than leopards. Also, the rosettes on their patterning are larger, less closely packed, and usually have black dots in the centres. Jaguars also live in America, while leopards live in Asia and Africa.

The jaguar, just like the tiger, is a good swimmer. It also has a very powerful bite, more so than the other big cats. This allows jaguars to kill prey by biting through their skulls. Jaguars have short tails and legs and are quite stocky, but they are powerful and sturdy.
Panther(leopard)
There is no actual species called the panther, however "panther" is a name given to either leopards or jaguars that have all black coats, due to an excess of the dark pigment melanin. They can also be referred to as melanistic leopards or melanistic jaguars.

While the coat is usually all black, sometimes the rosette markings can just be seen if you look closely (not recommended in real life!)
Puma
Pumas are also known as cougars, mountain lions, catamounts, and over 40 other local names. They can be found all over — from Canada all of the way down to the southern Andes of South America. The puma is in the feline family, and is native to the Americas. It is more closely related to the domestic cat than to a lion.

The puma is nocturnal and hunts a large variety of prey, including deer, moose, cattle, horses, and even rodents. Pumas are the largest of the small cats and have a recognisable facial characteristic of a black ring reaching from the corners of the mouth and around the nose.
Cheetah
The cheetah is a large-sized feline found in Africa and southwestern Asia, and is the fastest land animal in the world. They can reach speeds of around 72mph in short bursts but cannot run long distances.

Cheetahs are slender in build with a narrow waist, deep chest, and a proportionally small head. Their fur is short and coarse, and has a pattern of evenly spaced black spots. They have black stripes on their faces, which run from the inner corners of their eyes down to the corners of the mouth. These dark areas help keep the sun out of their eyes to help them with their vision for hunting.

Cheetahs usually hunt during the day, when lions are not very active. Their success rate is good, with a kill being made for every other attempt.

Cc:lalasticlala

Nice one OP. Very informative but you did not mention the LYNX. Although it is closely related to the puma but smaller in size.