"Lag" refers to large ping time on the internet. It's also been "adopted" to mean a slow computer. But Bluetooth? What do you mean by laggy? Syncing to lips in a video? The audio in the phone has to be converted to digital packets, then sent to the earphones or speaker over Bluetooth, then converted back to analog to feet it to the earphone or speaker. That inherently causes a bit of lag. (Turn 2 TVs connected to the same cable to the same channel and listen to the audio - there's a different amount of lag in each. [But TVs have delay lines, so their video and audio lags are the same. You can't do that with earphones, because the phone doesn't know how much lag the earphones have.])