It is derived from the word inshaqqat in the first verse.
Inshaqqat is infinitive which means to split asunder, thereby
implying that it is the Surah in which mention has been made of
the splitting asunder of the heavens. This too is one of the
earliest Surahs to be revealed at Makkah. The internal evidence
of its subject matter indicates that persecution of the Muslims
had not yet started; however, the message of the Qur'an was
being openly repudiated at Makkah and the people were refusing
to acknowledge that Resurrection would ever take place when they
would have to appear before their God to render an account of
their deeds. Its theme is the Resurrection and Hereafter. In the
first five verses not only have the state of Resurrection been
described vividly but an argument of its being true and certain
also have been given. It has been stated that the heavens on
that Day will split asunder, the earth will be spread out plain
and smooth, and it will throw out whatever lies inside it of the
dead bodies of men