The "type" means whether it's a consoleport, a frontport, an interface etc.
Tested with 2.10.3: go to /dcim/cables/import/, and you'll see a table "CSV Field Options" at the bottom. The row "side_a_type" has a question mark at the right hand side. Click on it.
The value you need is "dcim.consoleport", "dcim.frontport" etc.
It's a quirk of the Netbox data model that you can't just say "connect to device Foo port Bar"; you need to qualify Bar with its type. This is because each type of port is distinct: you can have an interface called "Bar" and a frontport called "Bar" on the same device. However, this does allow you to have corresponding frontports and rearports with identical names.