Enlightenment and four stages of enlightenment in buddhism

Enlightenment

It is a process of self realization. In other words, it is an insight or awakening to the true nature of reality. This experience generally occurs during intensive meditaion, when the attention has become one-pointed. Buddha Identified four different levels of attainment, each marked with deep and accurate experience of selflessness.

The ordinary person

An ordinary person is trapped in the endless cycling of world. One is reborn, lives, and dies in endless rebirths, either as a deva, human, animal, male, female, neuter, ghost, asura, hell being, or various other entities on different categories of existence.

An ordinary entity has never seen and experienced the ultimate truth of Dharma and therefore has no way of finding an end to the predicament. It is only when suffering becomes acute, or seemingly unending, that an entity looks for a "solution" to and, if fortunate, finds the Dharma.

Ten fetters in buddhism

1. Identity
2. Doubt in Buddha
3. Ascetic or ritual rules
4. Sensual desire
5. Ill will
6. Material-rebirth desire
7. Immaterial-rebirth desire
8. Conceit
9. Restlessness
10. Ignorance

The 4 Stages of Enlightenment

Stream-enterer

The first stage of enlightenment is called stream entry. The stream-enterer is also said to have "opened the eye of the Dharma. A stream-enterer reaches arahantship (last stage of enlightenment) within seven rebirths upon opening the eye of the Dharma. It is guaranteed that after achieving this stage, full awakening will be attained within the maximum seven rebirths and in the interim individual will not be reborn in any plane lower than the human (animal, preta, or in hell).

When you become a stream-enterer, you can never again believe that you’re really a separate self that lives inside your head and looks through your eyes.

Once-returner

The second stage of enlightenment is called once-returner. It means "one who once comes". The once-returner will return to the human world only one more time, and will attain Salvation in that life. Once returner, will return one more time to the realm of the senses excluding, of course, the planes of hell, animals and hungry ghosts. Both the stream-enterer and the once-returner have abandoned the first three fetters. The main difference between self enterer and once returner is that you have more control over lust, greed and delusion in once-returner stage.

Non-returner

The third stage of enlightenment is called non-returner. It means "one who does not come". The non-returner, having overcome sensuality, does not return to the human world, or any unfortunate world lower than that, after death. Non-returners are reborn in one of the five special worlds in Rupadhatu called the Suddhavasa worlds, or "Pure Abodes", and there attain Salvation. some of them are reborn a second time in a higher world of the Pure Abodes. A Non-returner has abandoned the five lower fetters, out of ten total fetters, that bind beings to the cycle of rebirth. 

Arahant

The last stage of enlightenment is called arahant. It means "a fully awakened person". A person who attained this stage has abandoned all ten fetters and will never be reborn in any plane or world, having wholly escaped world.
In Buddhism the term Buddha means ones who "self-enlighten" such as Siddhartha Gautama Buddha, who discovered the path by himself.