bhs stage 1, 2 etc can somebody explain these to me?

[sweuzo]

title says it all really, i keep hearing these but dont really know what they are exactly.

[Mehitabel]

http://www.bhs.org.uk/Content/Ods-More.asp?id=1799&pg=Education&spg=Information&area=2

click on the stage names in the flow chart and you get a description of them.