In geometry, a tesseract means the fifth dimension. In the world of A Wrinkle in Time, a tesseract is that as well, but also an exciting and dangerous way to travel through space and time, as the Mrs. W's and the children do. Mrs. Whatsit attempts to explain it exactly to Meg, Charles, and Calvin in Chapter 5, but a tesseract is essentially a shortcut between two points in space and time: a "wrinkle" in time. Mr. Murry and the U.S. government were experimenting around with tesseracts, and he was accidentally whisked off to the dark planet Camazotz; it is by tessering that the more skilled Mrs. W's take the children around the universe. When Mrs. Whatsit casually mentions a tesseract at the beginning of the story to Mrs. Murry, who turns white, she marks the beginning of the adventure to save Mr. Murry.
Tesseract Quotes in A Wrinkle in Time
The A Wrinkle in Time quotes below all refer to the symbol of Tesseract. For each quote, you can also see the other characters and themes related to it (each theme is indicated by its own dot and icon, like this one: Note: all page numbers and citation info for the quotes below refer to the Square Fish edition of A Wrinkle in Time published in 2007.).
Tesseract Symbol Timeline in A Wrinkle in Time
The timeline below shows where the symbol Tesseract appears in A Wrinkle in Time. The colored dots and icons indicate which themes are associated with that appearance.
...says yes, because she misses their father so much, and Mrs. Whatsit's mention of the tesseract has aggravated it. When Meg presses for a further explanation, her mother tells her that... (full context)
...they are also fighters against the Black Thing. They reveal that it is, in fact, tessering through the Black Thing that has caused Meg's injuries. Despite herself, Meg feels calm and... (full context)