Speed density refers to using qualified logarithmic tables for fuel and spark delivery instead of the computer adapting to a lot of sensor information. I guess this is done in radical situations or strip only applications but someone else here knows a lot more of the whys for speed density tuning than I do.

A live tune refers to modified fuel and spark delivery custom made using information gathered from your specific vehicle (either on a chassis dyno <also called a dyno tune> or on a safe section of road) to optimize the set up. The loose opposite is a mail order tune where a tuner uses safe averages and manipulates a PCM that is sent via the mail, etc. for installation by the end user with canned parameters.

Does that make sense?