Why is chicken considered meat?

(1) All meat is forbidden to cook with milk, except for the meat of fish and locusts. And it is forbidden to place it with cheese on the table, except for the meat of fish and locusts. One who vows [to abstain] from meat, is permitted to [eat] fish and locusts.

"A bird may go on with cheese on the table, but is not eaten," in the words of Beit Shammai. And Beit Hillel says, "It does not go and it is not eaten." Said Rabbi Yose, "This is [one] of the lenient rulings of Beit Shammai and stringent rulings of Beit Hillel." About which table were they speaking? About a table on which one eats. But for a table where one sets dishes on it, one puts this next to this and does not worry.

(4) [A mixture of] the meat of a permitted animal with the milk of a prohibited animal is forbidden to cook and forbidden from benefit. [A mixture of] the meat of a permitted animal with the milk of a prohibited animal, [or] [a mixture] of the meat of a prohibited animal with the milk of a permitted animal is permissible to cook and permissible for benefit. Rabbi Akiva says, "Wild animals and birds are not [forbidden in mixtures with milk] from the Torah, as it says, 'You may not cook a kid in its mother's milk,' three times. It exempts the wild animal, the bird, and the prohibited domesticated animal." Rabbi Yose HaGelili says, "It is stated, 'You may not eat any nevelah[an improperly slaughtered animal of a permitted species],' (Deuteronomy 14:21) and it is stated, 'You may not cook a kid in its mother's milk,' (Ibid.). That which [may become] forbidden as nevelah is forbidden to cook with milk. A bird, which [may become] forbidden as a nevelah, one might think that it should be forbidden to cook with milk, [but] the Torah says, "In its mother's milk." This excludes a bird, which does not have mother's milk.

R. AKIBA SAYS, WILD ANIMALS AND FOWLS etc. But have not these been applied to Samuel's interpretations? — R. Akiba is of the opinion that a prohibition can be superimposed upon an existing prohibition; therefore no specific verse is necessary [to show that the prohibition of flesh in milk applies to] forbidden fat or [to the flesh of an animal] that died of itself; moreover [the prohibition naturally applies to] an embryo [for it] IS as an ordinary kid; consequently all the expressions are Superfluous and serve therefore to exclude wild animals, fowl and unclean animals.

R. JOSE THE GALILEAN SAYS, IT IS WRITTEN, YE SHALL NOT EAT OF ANYTHING etc.

What is the difference between the views of R. Jose the Galilean and R. Akiba?

The difference between them is as regards wild animals: R. Jose the Galilean holds that wild animals are prohibited Biblically, whereas R. Akiba holds that wild animals are prohibited Rabbinically.

Or, you may Say, the difference between them is as regards fowls: R. Akiba maintains that wild animals and fowls are not included In the prohibition of the Torah but are prohibited Rabbinically, whereas R. Jose the Galilean maintains that fowls are not even prohibited by the Rabbis. There is also [a Baraitha] taught to the same effect: In the place of R. Eliezer they used to cut wood [on the Sabbath] to make charcoal in order to forge an iron instrument. In the place of R. Jose the Galilean they used to eat fowl's flesh cooked in milk.

Levi once visited the house of Joseph the fowler, and was served with a peacock's head cooked in milk and said nothing to them about it. When he came to Rabbi [and related this]. Rabbi said to him: Why did you not lay them under a ban? He replied. Because it was the place of R. Judah b. Bathyra and I imagine that he must have expounded to them the view of R. Jose the Galilean who said: A FOWL IS EXCLUDED SINCE IT HAS NO MOTHER'S MILK

(4) Similarly, the meat of a wild beast and the meat of a fowl together with the milk of a wild beast or the milk of a domesticated animal is not forbidden according to Scriptural Law. Therefore it is permitted to cook it and it is permitted to benefit from it. It is forbidden to partake of it according to Rabbinic Law so that people at large will not be negligent and come to violate the Scriptural prohibition against milk and meat and partake of the meat of a kosher domesticated animal [cooked] in the milk of a kosher domesticated animal. For the literal meaning of the verse implies only the meat of a kid in the milk of its actual mother. Therefore, they forbade all meat in milk.