Abigail was a servant in the Proctor household, although she was fired by Elizabeth Proctor who suspected Abigail was having an affair with her husband.
John: Abby, I may think of you softly from time to time, but I will cut off my hand before I reach for you again. We never touched.
In the final act, Elizabeth says to John, ""I have sins of my own to count. It needs a cold wife to prompt lechery"… "I never knew how I should say my love. It were a cold house I kept." Along with the fact that she had been "a long time sick", this is the cause of John's affair with Abigail. Elizabeth blames herself for Johns affair with Abigail.
Abigail: Aye, but we did!