Genesis 7:2 says Noah took one pair of each unclean kind onto the Ark. The pair consisted of one male and one female, preserving each kind during the Flood.
The same passage distinguishes unclean animals from clean animals. Noah is told to take seven pairs of every clean animal and one pair of every kind of bird, while the unclean animals are represented by one pair. Genesis 6:19–20 gives a broader earlier instruction to bring two of every kind, which is why readers sometimes remember only a general pair-based count.
The classification of clean and unclean animals belongs to the biblical framework and is not a modern zoological taxonomy. The passage also does not provide a complete species list. “Kind” is the translation used for the category in the narrative, and its exact biological equivalent has been debated.