Mental shield

Mental shield is the ability to have a protective barrier in one's mind that protects oneself from any kind of mental or telepathic intrusion or attacks.

Bella Swan (Twilight)
Bella's gift allows her to shield herself and those around her from supernatural powers that affect the mind, which explains why most of their powers were useless against her when she was sti ll human. She had displayed this power since she was human and, by becoming a vampire, her shield was greatly intensified in strength. This power comes from her subconscious desire to protect her mind above everythign else and as long as she holds on to that desire, it makes the shield difficult to extract. Her father Charlie shows a less developed form of this shield; indeed, Edward finds him difficult to read but not completely closed off like Bella.

At one point, Bella uses her shielding power as a giant dome to protect her family and friends when the Volturi attempt to make a move on them, when she was enraged by Edward facing danger alone and she is forced to stay behind, with an antagonistic smile emitted from Jane to push her anger further. Freed from her desire to protect herself, she is able to shape her shield in any way she wills it, such as creating a giant protective bubble or wrapping it around her targets like plastic bags. When she shields others, her mind will form an extra shield to protect herself. Those she shields will also become a part of her, allowing her to feel them in a range without having to look. Bella can also remove this shield completely and allow vampires' mental powers to work on her if she so chooses, though it is more difficult than pushing it out.

Though her shield is powerful, it has many limitations: it has no effect against a physical attack, which makes it easy for an enemy to invade her shield and use their power on those she protects. Additionally, it has no affect against Alice's power of subjective precognition, Jasper's ability to control her mood, Benjamin's power to control the elements of nature, and Marcus's power to detect relationships, since her shield can only block psychic powers that are connected to the mind. The only person who is truly immune to her shield is Renesmee, who is capable of penetrating it.

Aro, the leader of the Volturi who "collects" vampires with useful talents, was so intrigued by Bella's ability to block mental power as a human that he  twice offered her a place among his guard. She refused both times. Because of her shield, Bella is considered one of the most powerful vampires alive.