I'm somewhat new to the world of mountain bikes and I'm seeing various terms to describe different bikes. What is the difference between all-mountain, cross country, freeride, and downhill? Are they just marketing words or do they represent actual differences in the bikes (or maybe a bit of both)? Are there any other types of mountain bikes I missed?
The following list contains the basic characteristics and differences for the aforementioned types of MTBs plus 2 types of bikes that you didn't mention. Note that I've tried to summarise and "average" the characteristics of modern MTBs used today by amateurs and pros. So 9 kgs for XC bikes means that you can easily find 8 and 11 kg ones.
Cross country (XC) bikes:
All mountain (AM) bikes:
Freeride bikes (FR):
Downhill bikes (DH):
Dirt Jump bikes (DJ):
Slope style bikes (SS):
If you can imagine a compromise between a mountain bike that is light weight and easy to pedal, versus one with that is strong and has lots of suspension travel to tackle rougher terrain you might get a diagram such as the one below.
As we go from category to category we get heavier bikes that are harder to pedal, but that can handle rougher and rougher terrain, bigger jumps, etc.
The diagram also shows overlap between the categories as depending on how the manufacturer set up the bike you can argue it could be considered to belong to one or the other category.
Caveat - I am sure some will take issue with the exact size and overlap of the different categories, but the figure is intended to be illustrative only.