[Zope] What "Maximum age of a cache entry (seconds)" means in RAM Cache Manager?

[Litao Wei]

I have read the zope book and zope online help about RAM Cache
Manager. But all of them didn't say anything about the parameter "What
"Maximum age of a cache entry (seconds)" mean.
It looks that this parameter like "Cleanup interval (seconds)", which
zope book explained as "The lifetime of cached results.". But what
this parameter mean? Would somebody give me an explaination?
Thank you.