f(x) is a function that takes a word as input and returns a value between 0 and 1, indicating the association of the input word with two concepts: objects and modes of transportation. It is selective for concrete objects and tends to return higher values for words that are concrete nouns, while for modes of transportation, it tends to return higher values for words that are related to vehicles.

Please let me know if you have any further questions or if you'd like me to run more experiments to refine the description.