Otta can mean:

• A working name leading to what became the SI prefix for 10²⁴. It apparently came from the Greek ὀκτώ, eight, because it was equal to 1000⁸. It had been informally introduced before 1991, date at which the real prefix, yotta, a deliberate variant largely chosen due to considerations of the symbol to use for it, was promulgated. See unofficial SI prefixes.

• In Norse mythology, Otta the Simple was Freya's lover.
• Otta, Norway, a Norwegian town in Gudbrandsdal, named for the river Otta .