Multiple I2C PORTs.

[djconcept]

Hello, I would like to understand the logic, on the board, I find 3 I2C ports:

I2C-0
I2C-1
I2C-10

When i make this: 

Code:

ls /dev/*i2c*

I receive this

Code:

/dev/i2c-1  /dev/i2c-20  /dev/i2c-21

what exactly is the link?

Thank you in advance for your support.