"Halal" is an Arabic word, generally means permit.

Using in term of religion means permit by religion rules.

For example, permit to eat, permit to drink, permit to do and etc.

"Halal" is an antonym word to "Haram" which is means forbid. If using in term of religion will be describe as forbidden by the religion rules. Forbid in Islam is a command from Allah and his prophet only and it's a main principal to all Muslim to follows without any objection. It's because Muslims believe in the permit thing by God which is always good and useful and forbidden things are dangerous and unhealthy. God created all the mankind, therefore he knows whether is good or bad to human, according to his allowance and forbidden.

After all, human found good point of the permit thing in religious way and bad things in forbidden. By the way, it is not a main point because what humans found can be changed but God's command never changed.

Islam is the main principal in the way of Muslim life, concerned from born to die.. Therefore, every action of Muslim should follow Islamic rules especially consumption. Allah has guided all the mankinds ;

"O mankind! Eat of that which is lawful and good on the earth, and follow not the footsteps on Shaitan.

Verily, he is to you an open enemy"

(Al-Baqarah : 168)

Allah guided to all the mankind to consume good foods that he suggested in this world compared as a gigantic dining table. And follow not the footsteps on Shaitan. Verily, he is to you an open enemy. Allah guided the believers ;

"O you who believe (in the Oneness of Allah)!

Eat of the lawful things that we have provided you with, and be grateful to Allah, if it is indeed he whom you worship.

He has forbidden you only

the dead animals, blood and the flesh of swine, and that which is slaughtered as a sacrifice for others than Allah."

"If one is forced by necessity without willful disobedience nor transgressing due limits, then there is no sin on him.

Truly, Allah is Oft-Forgiving. Most Merciful"

(Al-Baqarah : 172 - 173)

h Surah "Al-ma-idah" indicated to prohibited animals with more description;

"Forbidden to you are blood, the flesh of swine, and that on which Allah's Name has not been mentioned while slaughtering, and that which has been killed by strangling, or by a violent blow, or by a headlong fall, and that which has been eaten by a wild animal unless you are able to slaughter it."

(Al-ma-idah : 3)

This is aim to announce to the believer, Allah guide them to consume good foods that he provided for them. And it is indeed he whom you worship. That's a reason why everything has to be HALAL.