When people talk about cadence, they usually reference the rhythm of how a band plays, keeping a beat or keeping time.
In the world of sales and marketing especially in the area of marketing automation cadence means timing. Many people confuse it with frequency, but it's more dialed in, more granular than that. Frequency relates more to volume and the haphazard way that many organizations send content out, at random times to random people.
Cadence is the pattern of the content meaning it includes the number of marketing emails/blogs/case studies/texts/calls sent, the spacing between them, the actual content sent, and the audience that's receiving and consuming (if it's good content) what you are sending