Thread:Project:Support desk/MediaWiki and WMF?

On this page, there are folders named from REL1_1 to REL1_18 which must be MediaWiki v1.1-v1.18. However, there is also a folder called wmf which comprises of 1.16wmf1-4 and 1.17wmf1 and another folder called wmf-deployment. What is the difference between MediaWiki releases like REL1_16 and REL1_17 and versions in wmf?

What does phase3 mean? and what does tags and trunk mean under this directory]?

Thanks guys!