It is the abbreviation of Bridge Tied Load. It reverses the speaker both terminals to connect by using two amplifier circuits compared with a usual single amplifier. If without output coupling capacitor,it may has an advantage that output electric power quadruples.
Short for Moisture Sensitivity Level, MSL is a JEDEC (Joint Electron Device Engineering Council) standard established for the purpose of preventing device failure due to volumetric expansion of atmospheric moisture introduced into the resin package of semiconductor devices during reflow. The floor life of IC packages, during which the components must be mounted and reflowed after opening the moisture-resistant packaging, is broken down into 8 MSL levels.