So the there are some activities which always get on in Google:

(a) Google Caching (Usually daily but mostly after 3days interval)
(b) Google Pr Update (Not specific time line approx 30-45 days)
(c) Google Back Link Update (Not specific time line approx 30-45 days)
(d) Google Directory Update
(e) Google Algorithm Update

“When ever Google changes its algorithm or do some refinement in their algorithm that is called google update. After google's florida update google has started giving the names to their updates” . Some of the popular google updates after the Florida update.

(a) Florida Update 16th Nov 2003
(b) Austin Update 11th Jan 2004
(c) Brandy Update 11th Feb 2004
(d) Google Bourbon Update Part I May 2005
(e) Google Bourbon Update Part II
(f) Google Bourbon Update Part III 7th June 2005
(g) Jagger Update Part I (16th Oct 2005 to 7th Nov 2005)
(h) Jagger Update Part II (27th Oct 2005 to 6th Nov 2005)
(i) Jagger Update Part II (4th Oct 2005 to 18th Nov 2005)
(j) Big Daddy Infrastructure change