Why a post defining something that you can just look up in Wikipedia? Because I am not satisfied with any definition that I can find. The classic French herb mixture called fines herbes ("feen zairb") is not something that can be fully defined as a short list of four herbs, finely minced. And far too many so-called references on the web and in print, including scholarly dictionaries, rush to give their idea of which four herbs comprise fines herbes and many of these authorities' lists are at odds with each other.
What these lists fail to address is the spirit behind fines herbes. Fines herbes are those herbs that in traditional French cooking pair well with seafood, poultry, and other delicately flavored dishes. These are herbs that are finely minced and added at the last minute before service to add both grace and a lightness (I particularly like the French words for this concept: légèreté, délicatesse, grâce).
Years ago as a young man, like the current experts, I used to be certain what the correct four herbs were; however, the older I get, the more things tend to gray, not only my hair. In reality, each chef has a preferred number, combination, and ratio of fines herbes. Although four herbs are traditional, some chefs use more and some use less. Herbs that are more or less traditional are parsley, chervil, chives, tarragon, thyme, dill, and other similar (that is, delicately flavored) herbs.
My favorite combination is parsley, chervil, chives, and very young dill, in equal proportion. I think that chervil gives enough anise flavor to the mix without adding the oft heavy handed tarragon. [Aside: tarragon never was on my list of "delicate" herbs—it is a culinary beast capable of slaying many dishes.] Very young dill is just the ticket for me. But naturally my mix varies depending on what I am cooking, what herbs I have on hand, and what season it is.
What you can infer from my list above is that assertive herbs such as rosemary and oregano do not belong in fines herbes, nor does cilantro which is highly alien in classic French cuisine. Could lemon balm or lemon verbena be a part of my fines herbes mix? That's a definite yes. What about bay? No, it's very pungent. Basil, no, I think not.
I hope you are starting to recognize the picture that I am trying to draw for you. Fines herbes is about fresh, tender, delicately flavored herbs that work well with mild dishes such as poultry, seafood, eggs, clear or cream soups, and salads, added at just the last moment for a touch of freshness and lightness. You would be served well to remember this and forget about the canonical list, which does not exist and probably never did.