what is the apple security center? telephone

Not enough context. But if it's anything that arrived in an email or text, was a popup in your browser, or a web page that opened to some dire warning, it's not Apple. They have no such department.

Any and all such instances above will be a scam. DO NOT call the number.

I've owned and used Apple products for 33 years and never heard of "Apple Security Center."

Did someone call you saying they were from Apple Security Center? If so, it is a scam, not Apple.