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.
Yes, products not listed in lineups on the website or catalogs/short forms are considered discontinued/obsolete. However, some discontinued products that have been delivered in mass quantities to certain customers are still being supported. (Please note that there may be delays in the case of samples purchased or products obtained through distributors.)