OL is a loanword from English. The acronym is based on the expression “office lady.” The term came into vogue during the high-growth years of “The Japanese Miracle.” At this time, male Japanese salaried workers began referring to themselves as bijunesuman / ビジネスマン, a borrowing of the English “businessman.” For a brief period, female Japanese office workers were called “business girls.” However, the unsavory connotations of “business girl” in English led to a cessation of this usage. The replacement term, “OL,” was coined, and it has remained in use ever since.
The title of OL is usually reserved for young, single women who perform clerical duties in an office setting. It would not be used, for example, in reference to a female factory worker, or a woman who was pursuing a more advanced professional career track. There is also an unwritten rule that once a woman reaches a certain age, she can no longer be called an OL. There is no absolute standard here, but the cutoff age is generally around thirty or thirty-five.
If you visit a Japanese office, the OLs will be easy to spot. In most companies, they are still required to wear uniforms. These women perform the standard clerical tasks that need to be done in any office in the world: typing, making copies, data entry, filing, etc. OL work is generally not a long-term career, and the field is dominated by women in their twenties. OLs typically work in these clerical positions for a few years while they are single, then quit when they get married.
There is a certain undertone of sexism in the term “office lady,” and this realization is not lost on many of the Japanese women who actually work as OLs. However, beyond the appellation itself, there is little to distinguish these workers from clerical office workers anywhere in the world. Moreover, it is worth noting that professional track careers are increasingly opening up to women in Japan.