(in Hindu and Buddhist tradition) an immense period of time, reckoned as 4,320 million human years, and considered to be the length of a single cycle of the cosmos (or ‘day of Brahma’) from creation to dissolution.
The current kalpa, called the Varaha kalpa, is the first day of Brahma's 51st year.
It is because you and I are defiled that we have been wandering lost and confused through samsara for limitless kalpas; and that we cannot immediately cast off wrong thinking and see our original nature.
So he knows that it is almost the same every time, but the pastime is a little different in each kalpa.
Old and new lie next to one another, mixed and intermingled; the ancient is about to pass away, while the modern is geared for eternity, or at least for a kalpa which seems to us eternal.
The first of these is that the Buddha was born within the current kalpa.