What is this key for? What is it called?

What country is this mac from?

On my MBP it doesn't have a symbol, but instead says "enter," and has the exact same functionality as the "enter/return" key.

It's there for using the numpad. If you hit "num lock," then use keys 7,8,9,u,i,o,j,k,l,m,. it turns into a numpad equivalent to what's on the right edge of desktop keyboards. Much like a desktop, while you're using the number subscripts on these keys, there's always an enter key at the bottom right edge (makes it easier for entering long sets of numbers).

Even without num lock on, this secondary enter key still functions just like the primary enter key for regular functions.

The enter and return keys are not always the same function. Whether the enter key works differently depends on the particular laptop. I have some mac laptops where the enter key did not work as it does on a desktop, but my current MacBook Pro does work as expected.

Here is one difference. In MS Word, Shift+Enter inserts a page break, Command+Enter inserts a section break. Shift+Return does not have the same function.

There are probably other applications which distinguish between Enter and Return.