What does "segmentation fault (signal 11)" mean in a TFM simulation

Hi Dear All,
I got such an error when I tried to run a TFM simulation for a gas-liquid system. What does it mean? Any clue is appreciated. Thank you.

A segmentation fault could mean literally anything. If you can, please attached the project files.

note that mfix is typically used for gas-solids flows, the constitutive relations may not be appropriate for gas-liquid flows

Thank you for your remind. I closed the calculation of KTGF for the gas phase, and used a constant viscosity. The plastic stress was shut off too.

Okay, I will attach it later. Thank you, onlyjus.