SDA is a data line. SCL is a clock line. Both are for the Wire library, which is an I2C protocol. These things you could find with a google search of “SCL arduino”. None of these labels are specific to the Mayfly, but they are Arduino basics.
AA is auxiliary analog, found that in the Mayfly Data Logger Features (I’ve personally never had to know what’s different about AA than the other analog ports, because I haven’t used an analog sensor in several years of data logging):
The thing is, there’s a huge knowledge base for all of this stuff online and I’m just doing my best to direct you to it. It’s finals week at my institution, and most of the people on these forums are volunteering their time, so it’s also tedious to answer questions that you’ve spent weeks building into a curriculum.