Contrary to what many English speakers seem to think, English is not the only language from which Japanese imports words and phrases - and often twists the meanings of. Ever since the Meiji Restoration, and even before that, Japan has been incorporating words from other languages very freely.
Which leads to today's word: アルバイト (arubaito), or バイト (baito) for short. German speakers may recognize that this comes from Arbeit. While Arbeit means 'work' (verb form to work is arbeiten), once again the Japanese imported version of the word is a bit different from the original.
アルバイト means part time or casual work, usually by students or other young people who can't or won't work at a 'real' or full time job.
The Japanese word for work is 仕事 (しごと shigoto), but someone who is working part time doesn't refer to their workplace as a 仕事先 (しごとさき shigoto saki) as a full time employee would; they'd call it a バイト先 (バイトさき baito saki).
When they go off to their job, they might say 「バイトに行ってきます」（baito ni itte kimasu), not 「仕事にいってきます」(shigoto ni itte kimasu).
'Proper' employees vs. バイト and others
In Japanese working society, a 正社員 （せいしゃいん seisha-in) is a full time employee, literally translated as a 'real' or 'proper' company member. Being a 正社員 means that one gets full benefits, a year-end bonus, and historically (though not since the early '90s) lifetime employment.
Then there are the other workers, which are called バイト、パート (paato, or part time, usually applied to housewives with part time jobs and never to men for some reason) or 派遣社員 (はけんしゃいん haken sha-in, or contract worker). Both バイト and パート workers work part time, and contract workers usually work full time, but without the benefits or year-end bonus. They also may or may not get paid for overtime. (Many employment agencies give benefits and other perks to contract workers who are signed up with them, however.)
Traditionally, being a 正社員 has had higher status than being another type of worker. But since the 'Lost Decade' of the late '80s to '90s, when the Japanese economy went through a big downturn, many younger people have preferred to earn their living by being 派遣社員 or even アルバイト. It gives them far more freedom to leave a job if they don't like it, take time off to travel, and so on. This is a huge fundamental change in Japanese society, which has been analyzed to death in Japan itself but doesn't get that much publicity outside of the country, even in the latest flurry of news stories trying to learn some lessons from the Lost Decade to deal with the current worldwide recession. In any case, the Japan of the Economic Miracle of the '60s to mid-'80s is long gone for all purposes...
