Spotlight Search has been completely redesigned in Yosemite from the old Spotlight Menu function. You can still search for files, but in addition you'll get information from the Internet such as movie times, Wikipedia, maps and recommended web pages. You can also do unit and currency conversions and math. File searches can be filtered by kind and date. You can also use logical functions like OR and - (not) to get better results. Find out all you can do with Spotlight Search in Yosemite.
Want to know more about Spotlight Search? Apple has a useful overview and some more information about narrowing your file search.