Previously templates expressed the indices that they should match using a glob style pattern in the template field. They should now use the index_patterns field instead. As the name implies you can define multiple glob style patterns in an array but for convenience defining a single pattern as a bare string is also supported. So both of these examples are valid:

PUT _template/template_1
{
  "index_patterns": ["te*", "bar*"],
  "settings": {
    "number_of_shards": 1
  }
}
PUT _template/template_2
{
  "index_patterns": "te*",
  "settings": {
    "number_of_shards": 1
  }
}