Is it forbidden for a male person to have feminine job? If so, how is a feminine job defined according to halacha?
Likewise, is it forbidden for a female person to have a masculine job?
Perhaps we could look at the question from a different angle. If a male were to work in a field which is predominantly female, then presumanbly he would come in contact with a lot of woman.
Assuming that is the case the Gemara in Kiddushin (82a) prohibits such occupations:
לא ילמד אדם את בנו אומנות נשים
"A person should not teach his son a trade that requires that he be among women."
If a man's profession requires that he be constantly with women (and often alone with these women), it can result in sin. The Talmud lists trades that require that a person often be alone with women: Our Rabbis taught: Whoever’s business is with women has bad character, for example: goldsmiths [who make jewelry for women], carders, handmill cleaners, door-to-door perfume salesmen, barbers [women bring their children to him for haircuts], launderers, bloodletters, bathhouse attendants, and tanners [who make clothing from skins for women]. These cannot be made appointed neither as kings nor as high priests. Why? Not because they are legally disqualified; but because their profession is undignified (Babylonian Talmud, Kiddushin 82a). The Talmud (Kiddushin 40a) relates the story of Rabbi Kahana who used to sell baskets to women. One day, a Roman matron tried to force him to have illicit relations with her. To escape, he went to the roof and flung himself from it. Elijah the prophet caught him and complained that he had to travel a distance of four hundred parsangs to save him. Rabbi Kahana explained that it was his great poverty that caused him to go into this line of work. Elijah gave him a vessel filled with golden dinarim. (translation and explanation from this site).
Although there is no mention of women working in predominantly male occupations which would bring her into contact with them, nonetheless, IMO, the underlying essence and spirit of the Rabbis concern as quoted above, would apply equally to women just as much as men.
In summation, there seems to be no such thing as a male job, or a female job in halacha, but rather jobs that are conducive to spirituality as summarized by the site linked above:
SUMMARY AND CONCLUSION
The ideal occupation has the following characteristics:
(1) It provides an individual with time to pursue spiritual pursuits.
(2) It does not tempt one to become dishonest or sexually immoral.
(3) It allows one to help people and society.
(4) It is profitable and enables one to become wealthy.
(5) It is clean, pleasant, and dignified work.
(6) It is not overly strenuous.