Jodu Māte or Jods is an equivalent being to the Devil or Velns in Latvian mythology. It does not have a special name or translation in English. Jodi (the plural form) are evil spirits that figure around in Latvian folklore. It is not clear, what they do or what are their actions as evil - they are just evil spirits... Their antagonist is Pērkons, and they are said to particulary appear in the time of thunder.
Superstition
Because of the tales of Jodu Māte appearing in thunder, when Pērkons is following her trying to catch her, the people tried no to leave buckets and cups opened - they say, that Jodu Māte will hide in them and then the lightning will strike exactly in the house where she is hiding.