What is type 'pubkey' in a scriptpubkey output from getrawtransaction?

What is type 'pubkey' in a scriptpubkey output from getrawtransaction?

Here is an output from getrawtransaction:

{
  ...
  "vout": [
    {
      "value": 12.50000000,
      "n": 0,
      "scriptPubKey": {
    "asm": "03d81b3d2ac76e322dcb2e713cb8fdeaf68cb83406c0e4d28dcd10a880ef172a6a OP_CHECKSIG",
    "hex": "2103d81b3d2ac76e322dcb2e713cb8fdeaf68cb83406c0e4d28dcd10a880ef172a6aac",
    "reqSigs": 1,
    "type": "pubkey",
    "addresses": [
      "mwzWcEU4kBkJPSTgB8LSBfvyaEjdXmyGh7"
    ]
      }
    }, 
    ...
  ],
  ...
}

What is a pubkey type? I could not find any reference to this.

Here is the output of decodescript on the script:

{
    "result": {
        "asm": "03d81b3d2ac76e322dcb2e713cb8fdeaf68cb83406c0e4d28dcd10a880ef172a6a OP_CHECKSIG",
        "reqSigs": 1,
        "type": "pubkey",
        "addresses": [
            "1HUZKBP5wAK3cKz4TZN4MkieiF8vbyNvpE"
        ],
        "p2sh": "3469piMXSTikVAdrSC791pQGxQb8pNXhua"
    },
    "error": null,
    "id": null
}

http://ift.tt/2AoUD8I