The leaky pipeline is a metaphor for the way that women disappear from some geeky careers (especially STEM) and hobbies.
The metaphor is that if you pour water (young girls) into a pipe, and it leaks along its length (girls and women exit at various times), very little water (professional women leaders) will emerge at the end of the pipeline.
The metaphor is often used to argue that if only later leaks in the pipe are patched, there will still be a relatively small number of women leaders emerge at the end, because of earlier leaks from the pipeline. This is true as far as it goes, but sometimes it is used to argue that until the early leaks are fixed, no one should pay attention to later leaks because it's a waste of time.
This last piece of reasoning is problematic:
- unlike a literal pipe leaking water, girls and women are not permanently lost to geekdom if they temporarily exit it, it is possible that girls and women who left or took a break will return
- unlike a literal (closed) pipe containing water, girls and women are not permanently lost to geekdom if they don't enter as, say, a 5 year old, they can enter at any point in life
- if girls and less experienced women see no women role models in leadership positions, they have less ability to picture themselves occupying such positions
- women in leadership positions may take an interest in the development of other women in a way that many men do not (although see Second shift)
The pipeline metaphor can play into Let's help the girls. Geek feminists argue that working simultaneously on multiple leaks from the pipeline is the better solution.
The pipeline metaphor can also lead to the perception that any woman leaving a geeky field is a tragedy. A goal of 100% retention is unrealistic and potentially coercive: people change fields and interests throughout their lives. That's fine. The problem is discrepancies between the retention rates of people of different genders, or between privileged and oppressed people, not an inability to retain everyone.
Finally, the pipeline metaphor connotes a belief that the end of the pipeline (presumably, either being a professor or researcher in a STEM field, or working in industry as a scientist or engineer) is a desirable place for women (or anyone else). This may not be true, as even women who have risen to the highest possible status in their field often continue to experience harassment and sexism. As Ashe Dryden asked (quoting Emily Strickland), "Should we be encouraging women to get into the pipeline when we know the pipeline leads to a sewage treatment plant?"