From TalkBass Wiki
1) typically associated with speakers and literally the amount of air it moves which effects the sound projected.
2) Open or reflective of exhibiting spaciousness/distance. Ant. Compressed.
Also, "A.I.R." (Acoustically Integrated Recording) technology patented by Line6. A.I.R. is a modelling algorithm that emulates various cabinet and microphone combinations. When combined with a preamp, amp, cab, and bass model, the D.I. result emulates a mic'ed bass rig in a studio or on stage, but with instant and infinitely variable parameters. Line6 recommends including the A.I.R. settings in a signal chain when running direct for a more life-like tone. When running into a cabinet (as on a stage), the A.I.R. settings can be disengaged.
