In Elasticsearch, there is no dedicated array type. Any field can contain zero or more values by default, however, all values in the array must be of the same datatype. For instance:

Arrays of objects

Arrays of objects do not work as you would expect: you cannot query each object independently of the other objects in the array. If you need to be able to do this then you should use the nested datatype instead of the object datatype.

This is explained in more detail in Nested datatype.

When adding a field dynamically, the first value in the array determines the field type. All subsequent values must be of the same datatype or it must at least be possible to coerce subsequent values to the same datatype.

Arrays with a mixture of datatypes are not supported: [ 10, "some string" ]

An array may contain null values, which are either replaced by the configured null_value or skipped entirely. An empty array [] is treated as a missing field — a field with no values.

Nothing needs to be pre-configured in order to use arrays in documents, they are supported out of the box:

PUT my_index/_doc/1
{
  "message": "some arrays in this document...",
  "tags":  [ "elasticsearch", "wow" ], 
  "lists": [ 
    {
      "name": "prog_list",
      "description": "programming list"
    },
    {
      "name": "cool_list",
      "description": "cool stuff list"
    }
  ]
}

PUT my_index/_doc/2 
{
  "message": "no arrays in this document...",
  "tags":  "elasticsearch",
  "lists": {
    "name": "prog_list",
    "description": "programming list"
  }
}

GET my_index/_search
{
  "query": {
    "match": {
      "tags": "elasticsearch" 
    }
  }
}