Based on the tests I ran, here is a description of the function implemented by f(x):

[DESCRIPTION]: The function seems to be selective for words that are associated with specific concepts. It assigns each word a value between 0 and 1, where a value closer to 1 indicates a stronger association with the concept. 

Let's analyze the results of the tests:

- "voting" has a low value of 0.0005, indicating a weak association with the concept.
- "racket" has a high value of 0.9433, indicating a strong association with the concept.
- "weather" has a low value of 0.0020, indicating a weak association with the concept.
- "outgoing" has a low value of 0.0014, indicating a weak association with the concept.
- "83%" has a moderate value of 0.0628, indicating a moderate association with the concept.
- "beats" has a moderate value of 0.0233, indicating a moderate association with the concept.
- "democracy" has a low value of 0.0002, indicating a weak association with the concept.
- "highway" has a low value of 0.0004, indicating a weak association with the concept.
- "Hollywood" has a low value of 0.0005, indicating a weak association with the concept.
- "tennis ball" has a high value of 0.9866, indicating a strong association with the concept.

Based on these results, it is difficult to pinpoint a specific concept that the function is selective for. However, it seems that the function may be selective for words related to sports, as "racket" and "tennis ball" have high values indicating a strong association with the concept. The function also shows some level of association with words related to numbers, as "83%" has a moderate value indicating a moderate association with the concept. 

Overall, the function appears to assign higher values to words that are closely associated with a particular concept, while assigning lower values to words that are less closely associated with that concept.