What is the core metric type in Prometheus used to represent a single numerical value that can go up and down?

A Summary samples observations and provides a total count, sum, and configurable quantiles, rather than a single fluctuating value.

A Counter is a cumulative metric that only ever increases or is reset to zero on restart, unlike a value that can arbitrarily go up and down.

A Histogram samples observations and counts them in configurable buckets, providing distributions of values rather than a single point-in-time value.

A Gauge in Prometheus is a metric type that represents a single numerical value that can arbitrarily go up and down, making it suitable for values like current temperature, memory usage, or queue length.