In the world of Wyndham's novel The Chrysalids, the "chrysalids" themselves are the children strewn all over the world who have a particular ability, regarded as a "blasphemy" in their post-apocalyptic and backwards culture. The children are telepathic, or able to communicate with each other over long distances. The group of telepathic children are supported by some sympathetic adults, but for the most part, "blasphemies" are forced to flee to the Fringes, as the mainstream people believe blasphemies will cause another "tribulation" or apocalypse.

As described in the previous answer, the word "chrysalid" is itself a variation on Latin chrysalides, and to the modern mind it first evokes the state in which a pupa finds itself while it is transforming into a butterfly or moth. If being in a chrysalis is, then, a state of transition or evolution, the Chrysalids in this story represent the changing state of the world depicted. They are also, more literally, in a state of evolution themselves, as, at the beginning of the novel, the telepaths are all struggling to fit into a world that rejects them, by keeping their abilities hidden. Meanwhile, by the end of the story they have gained the strength and increased telepathic power to reach out and find each other and the more advanced people on the other side of the world, in Sealand. The story, then, is the process of their own individual chrysalis or metamorphosis.

chrysalis

— n  , pl chrysalises , chrysalides
1.     the obtect pupa of a moth or butterfly
2.     anything in the process of developing

[from Latin chrysallis, from Greek khrusallis, from khrusos meaning gold, of Semitic origin; compare Hebrew harūz gold]
(Collins English Dictionary)

"Chrysalids," as in Wyndham's title, is a variation on the spelling of the plural form of the scientific word chrysalis. The correct spelling is, as above, chrysalides. A chrysalis is the hard-shelled pupa, or obtect pupa, of either a butterfly or a moth. A pupa is a life stage of metamorphosis for some insect, like the butterfly and moth. A metamorphosis is a radical change from one form to another seemingly wholly unrelated form; it is the change from a worm-like caterpillar to a winged beauty, a butterfly or a moth.

complete metamorphosis
insect development in which egg, larval, pupal, and adult stages occur, each differing greatly in morphology.
(Random House Dictionary)

Wyndham's novel, The Chrysalids, symbolizes (1) the complete metamorphosis society was forced to make after the cataclysmic catastrophe that destroyed life as it had been known and (2) the new complete metamorphosis that society was on the brink of making whereby a mutation favoring telepathy becomes the new sensory morphology of humankind.