A z-score is a number that tells you how many standard deviations a value sits away from the mean of its distribution. A z-score of +2 means the value is in the top 2.5% of the distribution; −2 means the bottom 2.5%. Framler z-scores every factor across the live universe so a 70 means top-quintile relative to today's peers.
Formally z = (x − μ) / σ. Z-scoring is the standard normalisation that lets us compare value (whose raw scale runs from 0 to infinity) against momentum (which runs negative to positive). After z-scoring, every factor lives on the same axis and can be combined into a composite without one factor dominating purely because its raw scale is larger.