This word is sexually discriminating (性別歧視,), so please be warned accordingly. The word is not exactly nice (sorry ladies, I'm not trying to raise offence with this post...)
The definition on Skritter is partially correct, in that it does mean “career path,” but the part thats missing is how the girl advances her career. Simply put: the lady uses her breasts to entice a higher boss in a company, do some sexual favours, and thus advance her career. The narrow slit between a ladies' breasts look like a path, hence the use of this word as “advancing a career through sexual favours.” Women with larger breasts are deemed to have a larger path, which means advancing is easier, and because men are tempted by larger breasts, the boss will likely become more easilly enticed. My gf swears there are women in China who 事業線, but its not common.
Maybe the definition isn't incorrect, but perhaps some exploration of the characters is necessary in order to grasp the whole meaning. I THINK this word is slang, which is why I'm learning it (I want to master all the slang's in Chinese (比如:囧, 我了個去 等等))。!
Again: I hope this post does not stem offence (if it does, please feel free to remove it).
Be well!