Rahab was a woman of Jericho who hid the two spies Joshua sent to scout the city and, in return, was spared with her family when Israel captured Jericho.
Joshua 2:1 in the King James Version reads:
And Joshua the son of Nun sent out of Shittim two men to spy secretly, saying, Go view the land, even Jericho. And they went, and came into an harlot’s house, named Rahab, and lodged there.
The verse opens Joshua 2, at the start of the account of the two spies. Read it in context at Joshua 2:1, or the full chapter at Joshua 2. Encyclopedia entry: en.wikipedia.org/wiki/Rahab.