During the last Maunder minimum in a period of 28 years only 50 sunspots were observed

Spörer noted that, during a 28-year period (1672–1699) within the Maunder Minimum, observations revealed fewer than 50 sunspots. This contrasts with the typical 40,000–50,000 sunspots seen in modern times.<sup>[8]

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Maunder Minimum - Wikipedia

So, it appears that this might happen again around 2030 to whenever the Maunder Minimum ends this time. 50 sunspots in 28 years is a whole lot fewer than 40,000 to 50,000 in a modern 28 year period today.

It appears that the fewer sunspots observed the colder the sun's effect on the earth becomes during those periods. Hence this type of period is called now "a Maunder Minimum".