This word is in use in the modern times as it sounds less religious. But, what does it really mean?
Light definitely means knowledge. The person who is enlightened must have a knowledge. Is this any knowledge? No. Not Physics, Chemistry, etc. These are all great, but they are changing. A person should have a knowledge that is stable. It should not change, at least not change much.
But, what is the necessity of a knowledge that does not change much. Because, a human being is in a search of happiness always. And, in that search a human is trying to get knowledge that will provide him/her the clue that shall lead to a permanent happiness. That is why the knowledge should be permanent.
Now, most of the persons who get enlightened have a knowledge that gives you a permanent happiness. But, that knowledge states that permanent happiness will not come from the material things and their pursuit. Material things will give survival and comfort, but not permanent happiness. Now, some people do not like this knowledge and they go to another enlightened being who gives them what they want or they go after another knowledge.
There are some fake enlightened beings who make a compromise with the permanent knowledge and try to satisfy the people and get their own material happiness in return from the people, via money, name and fame. Thus, there is a Enlightenment business also.
But, there are some other people who are very wise in the worldly life and they provide good advice to the worldly people from their experience. These are also called enlightened persons. And, this works out well within material world, when people accepts some happiness and some sorrow.
Sometimes some people help social cause such as national freedom, emancipation of disadvantaged sections of society, etc. These are exceptional qualities. They are also called enlightened by a section of population. But, when the social cause is over, such people are not worshipped, but only respected.
But, the word Enlightened in Yoga means as follows. When a person gets any knowledge, that knowledge creates only material impressions of further material life. They never end and the thing that previously gave happiness does not give happiness after a while. This game never ends. This leads to a logic that material life shall never give permanent happiness and also material life shall never end in general. Then, such a person tries to get rid of all material part of living and seeks beyond the material. When that person finds the thing beyond material, then that person is called enlightened in Yoga. Very few people go to such a person to follow their advice because that advice is not what they want. But, sometimes, they worship that person posthumously!