Why are some calendar entries showing a line through?

[Lynne Posner]

entering from a board card, the entry as shown on the calendar has a line through the text.

[Jonny Adams · Accepted solution]

@Lynne Posner when the due date check box on a card has been checked as done then the card summary will display with a strike through it on the calendar view. 

[Lynne Posner]

Thank you so much!