Fake accounts
A scammer will create a fake account to look like someone else's account and make it look like your account. Then the scammer will try to get your friends and others to accept a friends request from them.
Each account has to have a name that cannot be a duplicate. However the display name can be the same as other accounts. That is because there is several people on Facebook that has (usually) the same name like Steve, Bob and such. There are many people with the same first and last name on Facebook. When you get a friends request or look on their profile to see if it is an actual account.
A scammer will create a profile with a name that is not taken. They will give it a title of the person they want to mimic (for example John Jay). They will use "John Jay" for the title.
The scammer will steal the photos (click for info) from John Jay. The scammer will then get the list of friends on John Jay's profile. Then will make the fake account look like John Jay's account. Once they get that done, they will send friends request to John Jay's friends.
The scammer will hope that Jay's friends will accept the friends request thinking it is John Jay.
This usually does not mean that your password has been hacked. However if this has happened to you, you should change your password to be safe.
If you get a friends request from someone you know is already on your friends request. Contact the person to see if he/she created a second account. If he/she did, then accept it but if he/she hasn't, then delete the request, and have him/her alert everyone as well as Facebook.