AARRR

Sales Funnel Metrics - Acquisition, Activation, Retention (esp Bounce rate), Referral, Revenue - 2007-12-31-McclurePirateMetrics

Apr'2011 - Allan Branch http://b.lesseverything.com/2011/4/19/conversion-goals-sounds-fancy-but-what-the-hell-are-they

Jul'2012: Quotes from 54 Start Up leaders on single thing that improved their conversion rate.

Retention Science hopes to catch at-risk customers and save them.

Note it doesn't specifically include Usage Frequency (DAU, WAU, MAU), but that's often a predictor of retention.