Occlumency is a magical skill in the Harry Potter series that allows a wizard or witch to protect their mind from external intrusion and influence. It involves training the mind to block out unwanted thoughts and emotions, making it difficult for others to read or manipulate one's mind. Practicing Occlumency is essential for those who face threats from powerful wizards, such as Lord Voldemort, who can invade minds and extract information. The technique requires concentration and mental discipline, often taught by skilled practitioners like Severus Snape to help students defend against mental attacks.