It means that there's no problem when no harm or damage is done, such as the time my sister-in-law stole the name we'd chosen for a boy and we both ended up having girls.

it is something like...no one was hurt so don't worry about it....usually said by the person who appeared to cause a problem if you want to get an example for it...i have to think about it...I never use it but have heard it..let me see.... if someone could use your help and you don't help them for what ever reason and the peron believes something terrible will happen but it doesn't then they get upset with you for not helping, but you know nothing terrible happened to them this is ---'no harm, no foul' hope u can understand