Fistula is an abnormal communication between 2 epithelial surfaces (organs or spaces). like vesico-vaginal fistula is b/w urinary bladder and vagina, recto-vaginal fistula is b/w vagina and rectum, etc. in women.
in males also fistula occurs. these should be treated on priority bases as they can cause serious effects.
Note: this post is a reply to justsalman's post, Mr.thakur may or may not have this disease, but nothing can be said without a complete examination. so u r advised to see a good surgeon.