It is an implanted device used to permanently prevent pregnancy. They put the device in the fallopian tubes. Tissues grows over it, which causes a blockage so that the egg cannot go any further and the sperm cannot reach the egg.
It is when a nickel coil is inserted in each fallopian tube. This causes scar tissues to build up around it, which blocks off the tube. Now eggs cannot get to the uterus. It is the first and only sterilization technique to have ZERO pregnancies during clinical trials. I had it done and LOVE it.