The term "ColdFusion" can refer to either Adobe's ColdFusion Server, or the ColdFusion language, CFML (ColdFusion Markup Language). CFML is tag-based language, like HTML or XML. It's made it's mark by being very easy to learn and use. Further, since Adobe owns the leading interpretor for ColdFusion, they've made CFML work really well when integrating other Adobe technologies, like Flash, Flex, Air, PDF, and so on. Using CFML code, it's extremely easy to generate PDF files that contain graphs, charts, or other data on the fly via a web interface.
Personally, I love the language, and I choose it over other languages like because it's very easy to get things done with it. I really like PHP, and especially Ruby, too, but CFML is just... perfect. =)
The CFML community is super-friendly too. You can always find non-criticizing and useful help on the OpenBD or Railo mailing lists.