I searched on the www.cisco.com homepage for the term: show interface output hang
And here is what I got as a quote from the documentation:
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Number of hours, minutes, and seconds (or never) since the interface was last reset because of a transmission that took too long. When the number of hours in any of the "last" fields exceeds 24 hours, the number of days and hours is printed. If that field overflows, asterisks are printed.