* Concrete: When referring to a specific belief system or religious institution, "faith" can be considered concrete.
* Example: "He converted to the Christian faith." (Here, "faith" refers to the Christian religion.)
* Abstract: When referring to the quality of trust or belief, "faith" is abstract.
* Example: "She had faith in her friend's ability to help." (Here, "faith" refers to the belief and trust she holds.)
Therefore, the categorization of "faith" as concrete or abstract depends on the specific meaning you want to convey.