# Concepts

### Lossless Aggregation

A method of aggregating observability data that preserves 100% the fidelity of the original data.

### Log Body

The body of the log entry. This value is displayed when browsing the log and usually indexed for full text search.

For JSON logs, the log body is usually represented by the value of the `message` key.

### Top Level Keys

Top level keys are the first level of keys in a json logs.

For example, take the following log:

```json
{
    "top": 1,
    "nested": {
        "inner": 2
    },
    "bottom": 3
}
```

In this case, `top`, `nested`, and `bottom`, would be top level keys

### Vector Remap Language (VRL)

[Vector Remap Language](https://vector.dev/docs/reference/vrl/) is a domain-specific language developed by [Vector](https://vector.dev/) for modifying your observability data.