Originally, the term cadence meant the rate at which a regular event recurs, possibly with variations, but with an overall cycle that repeats. For example, the cadence for team meetings might be "Every Monday, with a longer meeting on the last meeting of each month."
Project X is on a six-month release cadence, whereas Project Y takes two to three years between releases.
Q: What was the cadence of email requests you sent out to drive contributions?
A: We started with an announcement in September, with two follow-up messages in the next month.
In what I suspect is a case of I want to use this cool word other people are using, even though I don't know exactly what it means, the term has been applied more broadly to mean schedule or timeline, even for nonrecurring events. Sample usage: "What is our cadence for making this available outside the United States?"