Terri Mackleberry

Terri Mackleberry is the younger sister and twin of Sherri. She is in the same class with Bart at the Springfield Elementary School, although her and her sister often hang out with the second graders.

Biography
Terri and her sister are quite bright students and more than a little strange (they even have their own language). While they're conniving and mean, they're very close to the point where they're afraid to be separated and tend to hug when they're scared.

Terri and Sherri are also very mischievous. They love to cause trouble but unlike Bart, they rarely if ever get caught. Bart is one of their favorite targets. One time they kissed Bart, making him cause another disruption and be forced to sing on the bus. On another occasion, the gave him intentionally false information on American history; however, both girls correctly guessed that Bart had not prepared himself for a test and was looking to get all the answers from a student who studied, so the prank was arguably to teach Bart a lesson in slacking; since if he had studied, he would have realized the information was incorrect.

Terri appears to have a crush on Bart, as stated by her sister. However, nothing in particular has become of it yet. This could be down to Bart seemingly being more interested in Sherri, who does not return his feelings most of the time.

Their relationship with Lisa is especially complicated. Sometimes, they appear to be friends. Other times, they will reject or berate her. Most often, it's the latter. While they pretend to be friendly towards people they dislike they're far less subtle towards Lisa. While easy to assume they reject her for being "too smart" or "too weird" they themselves are both smart and strange. In addition, they have sometimes been seen interacting with kids such as Allison Taylor, Martin and even Ralph implying their hostility towards Lisa is more personal. On the few occasions where they appear to be friends, Lisa makes little effort to interact with them or even ignores them completely, which they have even complained about.

They have also done a few nice deeds for Lisa, like letting Lisa sit between them when nobody else let her have a seat or cheering her on.

Their social standing is just as inconsistent. They are sometimes lumped in with the popular girls yet they're rarely if ever given a voiced appearance amongst them. When they do take an active role in shunning Lisa, they're almost always alone and they have never led any groups of girls. In addition, Janey and all of the other girls they have interacted with, except for Allison and Alex Whitney, showed themselves to be every bit as fair-weathered to the twins as they are to Lisa. As such, their social status might only be slightly better than Lisa's.

Despite all of their similarities, they aren't always considered equals. Principal Skinner made it clear that in the event of a nuclear disaster he only intended to save Sherri but not Terri. Terri also once remarked about having a chance to step out of her sister's shadow, implying she feels unappreciated or inferior to Sherri.

Non-canon
It is revealed that in the future, Bart is in a relationship with Terri. When he accidentally makes out with Sherri; he asks, "Wait, you're not Terri?" and awkwardly backs away. It is unknown what became of this relationship.

Nelson Muntz simultaneously dated and impregnated both Terri and her sister, who bore him four children (two sets of twins, naturally) shortly before Nelson's high school graduation. He abandoned them during Bart's graduation party, using the same statement his father said to him before abandoning him.

The Simpsons arcade game
Terri appears in stage 1 and 2 carrying a plate of food for the Simpsons to gain health.

The Simpsons: Hit & Run
Skinner mentions that the school rabbit, and possibly Sherri and Terri, have been eaten by Lumpy in Level 4.

The Simpsons Game
Sherri and Terri were among the kids who bought copies of Grand Theft Scratchy and become violent. Alternate versions of Sherri and Terri are one of the holders of the three Sparklemon that Homer and Lisa must defeat. They are later among the enemies sent by God in "Game Over".

Creation
They have similarities to The Grady Twins (ghost girls) Danny sees in Stanley Kubrick's adaptation The Shining, of Stephen King's The Shining novel of the same name. In a deleted scene of the parody of The Shining called "Treehouse of Horror V", they are ghost twins seen by Bart. They also take on this role in The Simpsons Game where in a game engine elevator, they are heard saying "Come Play With Us Simpsons". She is said to be the taller of the two.

Trivia

 * Terri is the one on the right as it was stated by Matt Groening that Sherri is always on the left.
 * Both she and Sherri, bear some resemblance to the twins Selma and Patty Bouvier, as both hold an enjoyment for tormenting the males of the Simpson family, but for different reasons, and have a close relative who have a crush on one of the Simpsons.