This article is gonna be short, and it is directly connected to the article on "up or out". A terminal job means you are no longer in "up or out" mode, but rather can coast along this path for the rest of your career. We'll break down what exactly this means for you and your career.
Typically, you will reach terminal 5-10 years into a job. This is because when you're getting yourself established, you're often not contributing much to the bottom line, as you're inexperienced. However, around 5 years in you gain enough experience to be worth more than your salary, so companies are fine to keep you around doing the same old stuff. The best way to find out what terminal is in your company or profession is to see where the "for lifers" end up most of the time.
One major advantage is work life balance. Terminal jobs have great WLB because no job expects you to work 50+ hours while raising a family. Another benefit is consistency. You likely won't have major layoffs or shake-ups at this level. This, however, is most definitely not the level for type A people who are overachievers. It also has a lot of disadvantages from a salary perspective. It is worth noting that you will likely still see salary increases, but you'll see more salary benefits with job hopping and moving around.
So, say you find yourself here and you want more. Well, first, try to do more at your current job. If you're an individual contributor, look towards management programs, or alternatively look towards higher level/more advanced individual programs in the company. Alternatively, go to a new company. Startups are great for this because you can get a high level position super quickly. You can also take things slow and steady here. Another option is simply to go back to school. A masters or MBA will be good if your company will pay for it.