The name sutra (Sanskrit for "thread") in Buddhism originally was given only to the sermons of the historical Buddha. The sutras were recited from memory by the Buddha's disciple Ananda at the First Buddhist Council. From Ananda's memory they were collected in the part of the Tripitaka called the Sutra-pitaka.
For more about how the Tripitaka originated, see "The First Buddhist Scriptures: The Tripitaka or Pali Canon."
The Mahayana sutras, however, were most likely written no earlier than five centuries after the death of the Buddha, possibly later, which would seem to make them unlikely candidates for the title.
Even so, they were written in the style of the original sutras as if Ananda had recited them. Those later sutras considered essential texts by at least some Mahayana schools are included in what is called the Northern or Mahayana Canon of sutras.
To confuse matters further, there are some texts that are called sutras but are not. An example of this is the "Platform Sutra," which contains the biography and discourses of the 7th century Ch'an master Hui Neng. The work is one of the treasures of Ch'an and Zen literature. It is generally and cheerfully agreed that the Platform Sutra is not, in fact, a sutra, but it is called a sutra nonetheless.