SOA directives

[Lord Skeptic]

I apologize for the newbie question but I can't find any information on the 
net.

I have these settings for my domain (my admin set them):

        refresh = 10800 (3 hours)
        retry   = 1800 (30 mins)
        expire  = 3600000 (41 days 16 hours)
        minimum ttl = 259200 (3 days)

What is the meaning for each value?
Most importantly, which value do the foreign NS lookup to update their 
records for my domain?

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