Expresses a lack of appreciation; could hurt feelings if directed at a person. By not thanking her, he took her help for granted.
Pro Tip 2/3
Not Always Negative
When about objects, it may imply comfort with the consistent presence or function of something. With electricity always available, we take light for granted.
Pro Tip 3/3
Overlooking Effort
Suggests failing to acknowledge someone's effort or the complexity of a task. The boss took the team's hard work for granted.