The Symbiote Costume, also known as the Black Suit by fans, is the first brand new change of costume donned by Peter Parker in the first published Amazing Spider-Man #252, and chronologically donned in Secret Wars #8.
During Secret Wars, Spider-Man had his costume heavily damaged, and the other heroes pointed out to the room full of machinery to fix his costume. Once there, Spider-Man released the symbiote, and it covered his body, forming a new costume, completely black with a big white spider symbol on his chest, slightly larger eyepieces and white patches on the back of each hand. He wore this costume for the remainder of the Secret Wars.
It was revealed in Deadpool's Secret Secret Wars that Deadpool was responsible for releasing the symbiote costumes and wears the costume before Spider-Man, causing the suit while syncing on Deadpool's personality makes it more insane.
After the end of the Secret Wars, Spider-Man returned to Earth and brought the symbiote with him, there he discovered that the costume could mimic any clothing he wanted.
For quite some time, Spider-Man used the costume to fight crime, and the symbiote began to care deeply for him. Believing that he was helping him, the symbiote sneaked back into Peter's body after he had taken it off and gone to sleep. It would then carry the unconscious body of Peter through a typical session of fighting street crime silently. Thus for as long as he had the symbiote he would be inexplicably tired in the morning as his brain would rest but his body would be getting no rest at night. After witnessing the suit spontaneously webbing Felicia, preventing her from leaving (because she saw Mary Jane). Spider-Man decided to investigate on his new suit.
Upon going to Reed Richards, Peter discovers that the black suit he donned was actually alive and was slowly trying to permanently bond with Peter. Peter then removes the creature using high frequency sonic waves and the symbiote is imprisoned. However, not too long after, the symbiote manages to escape and hide in Spider-Man's closet, disguising itself as a normal Spider-Man costume, and successfully reattaches to Peter.
Panicked, Peter manages to swing to a church and ring the bells until the symbiote detaches, but he passes out. The Symbiote, in a last act of mercy, drags Spider-Man to safety in the undercroft, but decides to not bond with him again, and saddened, leaves.
Info gotten/taken from:http://spiderman.wikia.com/wiki/Symbiote_Costume