Massah (Hebrew: מסה) is one of the locations which the Torah identifies as having been travelled through by the Israelites, during the Exodus; although the list of visited stations in the Book of Numbers does not mention it. In the Book of Exodus, Massah is mentioned at the same time as Meribah, in a context which suggests that Massah is the same location as Meribah, but other biblical mentions of Massah and Meribah, such as that in the Blessing of Moses, seem to imply that they are distinct locations.
The Biblical text states that the Israelites argued with Moses about the lack of water, with Moses rebuking the Israelites for testing Yahweh, hence the name Massah, which means testing. In an earlier narrative concerning Marah, a similar argument is related, in which Yahweh tested the Israelites; some textual scholars regard this latter episode, which doesn't mention Massah explicitly, as being the Elohist version of the naming of Massah, while the former account, in which the name Massah refers to the testing of Yahweh by the Israelites, is attributed to the Jahwist.
O that today you would listen to his voice!
Do not harden your hearts, as at Meribah, as on the day at Massah in the wilderness,
when your ancestors tested me, and put me to the proof, though they had seen my work.