Mandatory and Basic are words that are used interchangeably.
According to the 802.11 standard, when rates are specified as "basic rates", it means that any client that wants to connect to an AP MUST be able to modulate on every rate that is specified as "basic". You may see this referred to as a "Basic Rate" in a frame capture, though it may also be called mandatory - it's the same thing in this context.
I set up a frame capture to illustrate for you:
When a Ruckus ZD WLAN is set up with default settings, the rates are set as:
After connecting and issuing the ofdm-only command, the data rates are set like this:
I hope this helps.
Neil