Aftersmoke is the time that the wick visibly smokes or glows after blowing out a candle at the end of a burning period. The aftersmoke will probably be slightly different for each burning period as your candle burns down. Wicks can often smoke or glow for longer at the end of the first burn period than for the rest.
The aftersmoke for a candle should be calculated as an average of the aftersmoke for every burn period of the candle. The average aftersmoke time should not be more than 30 seconds.

When the candle is extinguished, the wick can continue to smoulder, especially if there are carbon deposits present, which are often seen as a "mushrooming" at the tip of the wick. This smouldering is the result of the wick consuming the remaining combustible materials in its vicinity, even without an active flame. This produces the visible smoke known as aftersmoke.