According to Genesis 7, Noah took seven pairs of clean animals onto the Ark.
The instruction distinguishes between clean and unclean animals. Noah is told to bring seven pairs of every clean animal, consisting of a male and its mate, but only one pair of each unclean animal. The passage also gives the same seven-pair instruction for birds of the sky.
This detail occurs immediately before the Flood begins and differs from the simpler instruction in Genesis 6, which says that a male and female of every kind should enter the Ark. Readers and translations sometimes notice this difference and summarize the story as involving only one pair of every animal, but Genesis 7 adds the special provision for clean animals.
The distinction is connected with the post-Flood sacrifice: after leaving the Ark, Noah builds an altar and offers some clean animals and birds. The text does not provide a modern species count, so “seven pairs” refers to the biblical categories in the narrative, not a zoological inventory.