A continuous metric is a measurement of a value where the thing being measured always has a valid value at each measurement point.
For example, CPU percent busy is a continuous metric. For every sample CPU interval, a valid CPU percent busy measurement can be taken. A continuous metric differs from a count metric in that continuous metric samples cannot be added across time in a meaningful way. Instead, continuous metric samples use average, minimum, and maximum statistics. To determine how busy the CPU has been since midnight, average, rather than sum, the samples since midnight.