CALPHAD stands for CALculation of PHAse Diagrams, a methodology introduced in 1970 by Larry Kaufman. Originally based on computer calculation of thermodynamic functions and equilibria in multi-phase multi-component materials (such as alloys, ceramics, etc.), CALPHAD is now a much wider aprroach which uses several computational techniques (such as Abinitio Calculations, Machine Learning, Finite Elements, etc.) in order to simulate properties and behaviour of complex materials undergoing specific conditions and/or processes.   

More information about the CALPHAD approach:
Official CALPHAD website
CALPHAD in Wikipedia

Simplified CALPHAD flowchart