What Is Type (like "object") In ERC721 Metadata JSON Schema

According to the standard, there's a type such as "object" shown below. What is this type for and what other types can we use? Can I use like "art?"

{
    "title": "Asset Metadata",
    "type": "object",
    "properties": {
        "name": {
            "type": "string",
            "description": "Identifies the asset to which this NFT represents"
        },
        "description": {
            "type": "string",
            "description": "Describes the asset to which this NFT represents"
        },
        "image": {
            "type": "string",
            "description": "A URI pointing to a resource with mime type image/* representing the asset to which this NFT represents. Consider making any images at a width between 320 and 1080 pixels and aspect ratio between 1.91:1 and 4:5 inclusive."
        }
    }
}

It's the datatype of the described item according to the JSON Schema specification. It's a standard used in other development fields as well - not limited just to NFTs or blockchain development.

There is a list of default allowed type values: http://json-schema.org/understanding-json-schema/reference/type.html

It's possible to create a custom type in JSON Schema, but the limited scope of what the "ERC-721 Metadata Document" document allows, doesn't effectively allow for custom types.

TLDR: Cannot use type: "art" in an "ERC-721 Metadata Document". Can use it in a larger scope (e.g. a REST endpoint definition).