The Almighty God has decreed:
“He (God) has forbidden to you only what died itself (having not been slaughtered before it died), as well as drained blood, swine flesh, and that over which any name other than God’s has been invoked. Whoever falls into a state of necessity (and eats) without coveting anybody’s right or exceeding the limits of necessity, there is no sin upon them. Surely God is forgiving and beneficent.” (Al-Baqarah 2:173)
Further detail is given in the following verse:
“Forbidden to you is carrion, and blood, and the flesh of swine, and that over which any name other than God’s has been invoked, and the animal that has been strangled, or beaten to death, or killed by a fall, or gored to death, or savaged by a beast of prey, save that which you may have slaughtered while it was still alive; and [forbidden to you is] all that has been slaughtered on idolatrous altars.” (Al-Maida 5:3)
When we mention halal meat we must be careful about three issues:
1- Firstly, you must be sure that the meat is not swine flesh (pork) and does not contain any of its products (unless they undergo a chemical process that would transform them into another substance).
2- According to the verses above, an animal that dies itself before being slaughtered is forbidden to eat because its meat would become “carrion = maytah” and you would be eating a dead animal’s meat.
Most western countries oblige the stunning of animals before being slaughtered. It is important to know whether the animals are only stunned and not dead before being slaugtered, otherwise it would be forbidden to eat. Yet, in some of the western countries regulations provide that the animals that die during the stunning process on meat production chain cannot be used for consumption of human, because the blood that remains in the dead body toxicates the meat and eating that meat is harmful to human health. The dead animals are separated and used as animal food or for other purposes. In such a country, you would be allowed to eat meat products anywhere, as long as you learn that your meal does not contain pork or lard or other pork products (that dit not undergo a chemical process that would transform them into another substance).
If a similar regulation is not set by the government of the country you live in, you can not know whether the animals die before being slaughtered for consumption or not. You must do a good research on the slaughter regulations in your country. If there is not such a regulation, and the law allows the dead animals to be cut and used for human consumption, you are advised to stay on the safe side, and not eat out.
The same principle applies to the poultry.
3- Muslims are not allowed to eat the meat of animals that are sacrificed or slaughtered in the name of anyone other than God.
This third issue is one of the widest misconceptions in Muslim world, because most of the scholars assert that Islamic slaughter must begin with Basmala.
That is not the case according to the verse. Eating the meat offered by non-Muslims is not forbidden just because they are non-Muslim. It is lawful (halal) in this aspect as long as the animal was not slaughtered in the name of anyone other than Allah. So, meat of the animals slaughtered without Basmala, or slaughtered by machines or by Jews or anyone who does not sacrifice the animal to someone other than God are eligible to eat, as long as they comply with the first and second items mentioned above.
Considering all these three issues together, you are advised to learn the slaughter regulations in your country and decide what to eat accordingly.