Oftentimes when talking about a man's penis being cut off, people mistakenly use the term "castration". Here's some interesting and helpful information from a medical and historical perspective on the subject.

Penis removal - Wikipedia, the free encyclopedia

In ancient civilizations, removal of the human penis was sometimes used as a means of demonstrating superiority: armies were sometimes known to sever the penises of their enemies to count the dead, as well as for trophies. The practice of castration (removal of the testicles) sometimes also involves the removal of all or part of the penis...

...Some men have penile amputations, known as penectomies, for medical reasons. Cancer, for example, sometimes necessitates removal of all or part of the penis. In some instances, botched childhood circumcisions have also resulted in full or partial penectomies.^[6]...

...Issues related to the removal of the penis appear in psychology, for example in the condition known as castration anxiety. Others, who associate the organ with rape and male dominance and aggression, may consciously or subconsciously see the organ (their own or those of others) as a weapon and express a hatred for it, potentially desiring to see it violently removed...

...AssaultThere have been incidents in which men have been assaulted, usually by their sexual partners, by having their penises severed. The case of John and Lorena Bobbitt, for example, was popularly known for Lorena Bobbitt cutting off the penis of her husband, John, out of rage after he allegedly raped her, though he claimed it was for revenge when she discovered his infidelity. Bobbitt's penis was successfully reattached, and he later had a brief career in pornographic movies.

This was not the first modern case, however. On May 18, 1936, Sada Abe strangled her lover (believed to be at his request, he wanted to die while having sex) Kichizo Ishida and cut off his penis, placed it in her kimono and carried it around with her for days before eventually turning it over to the police. She spent a very brief time in jail, and was granted amnesty in 1940. The penis was last seen at a department store exhibition in 1949. This episode was the basis of the filmIn the Realm of the Senses.

Mutilation or forcible removal of the penis has special symbolic significance. As a symbol of male sexuality, fertility, and masculinity, the removal of the penis may be inspired by a desire to emasculate, and sometimes results in the emasculation of the victim. Another motive, particularly in cases of spousal assault, is sexual.

From 1973 to 1980 one hundred cases of Thai women cutting off their husband's penises were recorded.^[7] Most of them were not reattached.^[8]

A study of penis reattachment, found that of a group of 50 men, 98% reacquired functionality, even though some involved full reconstructive surgery using tissue and bone. Reportedly some of these men later fathered children...^[9]