MSOL (Median Spent Output Lifespan) is the median age (in days) of all spent transaction outputs. This indicator, along with ASOL, highlights (on a macro level) how many days coins were held before being moved, giving insight into short-term and long-term HODLer movements.
It should be noted that, in order to account for change and eliminate obvious relay transactions, outputs with a lifespan of less than 1 hour are discarded.
MSOL (Median Spent Output Lifespan) is defined as the median age (in days) of all spent transaction outputs in a given time period.
Glassnode - ASOL/MSOL Announcement