A time series in Prometheus is represented as follows:

<metric_name>[{<label_1="value_1">,<label_N="value_N">}] <datapoint_numerical_value>

As you can see, it's represented as a metric name, optionally followed by one or more set of label names/values inside curly brackets, and then the value of the metric. Additionally, a sample will also have a timestamp with millisecond precision.