FAQ: What is the meaning of the Ipopt printout (objective, inf_pr, inf_du, lg, d, lg(rg), alpha_du, alpha_pr, ls)?

See: https://drops.dagstuhl.de/volltexte/2009/2089/pdf/09061.WaechterAndreas.Paper.2089.pdf#page=10

In simpler words:

• inf_pr tells you how much the constraints are violated. If it is 0, then there are no constraints, or they are not violated.
• inf_du tells you how much the optimality conditions are met.

See also this lecture on Teachable.