The cartridge is the whole thing, the stylus or needle is what makes contact with the record.
http://en.wikipedia.org/wiki/Magnetic_cartridge
My personal rule of thumb is spend as much as possible. 
Some may disagree with this, but with turntables, et al, you actually do have to spend more to get more. Greater definition, greater transparency and so forth. But, the cheaper stuff can be musical also. And also, like headphones, different cartridges have a different flavor of sound. I highly suggest finding a price point and manufacturer you like and reading as much about everything as possible before you plunk down any cash.
Find a price point you're comfortable with.
And again, do you have a phono stage?