The inflationary use of the word "ally" has irritated and annoyed me for quite some time. It's inaccurate and accuracy is really desirable for a meaningful exchange of thoughts.
Americans and British appear to use the word much more often than actually warranted by "if you are attacked, we will fight with you" treaties. Germans don't use their respective word so indiscriminately, at least not in the context of countries.
One of the confusions which appeared because of the indiscriminate use of the word "ally" was about Turkey and Israel, with people asking why the U.S. government didn't staunchly support the U.S. ally Israel in its diplomatic conflict with Turkey.
Well, Turkey happened to be the true ally, and Israel being more the subsidised pet project of U.S. foreign policy. People talked of Israel as "ally" all the time*, though.
Actually, there's no treaty saying that Israelis should fight side-by-side with Americans, while Turkey is a member of NATO (admittedly, the relevant wording of the North Atlantic Treaty barely meets the definition of a real alliance).
It was the indiscriminate (if not wrong) choice of words which confused instead of informed.
The Strategist blog has published a post citing two studies about ally behaviours, and the difference between these studies' results (one with a loose definition of alliance, the other more strict) supports the importance of not mixing up political cooperation with military alliances: Real allies joined the fight on their allies' side in about three quarters of the cases, while with the very wide definition of "ally" it's only one quarter!
It would help a lot if "partner" was substituted for "ally" more often, as it's more accurate and less confusing in many cases. This could also help to give actual allies the respect they deserve for sticking as an ally even with overly aggressive great powers.
*: With one prominent exception, the CIA.