One of the challenges of the English language is that words tend to mean, to paraphrase Lewis Carroll, what specific professions have intended them to mean, which creates great confusion for learners, especially foreign ones. A fine example of this is the simple, three letter word bar. Derived from the old French word barre, meaning a long, rectangular piece, it has taken on so many meaning as to become complete unpredictable for a non-native.
In its simple form, a bar is a barrier. People can be barred from driving if they get too many tickets. If everybody is welcome, bar none, nobody feels bad. Being behind bars means being in jail or prison, a definite barrier. However, if someone raises the bar, it means that they have set a new standard of excellence, not created a barrier. Passing the bar exam means you now become part of the bar, the society of lawyers. Even more confusing, rebar almost always refers to the metal rod inserted into cement to create reinforced cement, not a second cancellation of rights. In modern slang, it is so foggy that you can see your own hand, barred means just that, not an allusion.
As the second noun in a compound noun, ambiguity takes over. A bar, including a wine bar, is a place to drink alcohol in pubic. A chocolate or health bar is a tasty snack wrapped in plastic. So, what is exactly a milk bar? The first actually applies most of the time since it is a public drinking place that does not serve alcohol, as strange as that may seem. On the other hand, there are edible milk bars. Just to confuse matters, an iron bar has nothing to do with either use and instead is a heavy piece of metal used in construction. For that matter, a music bar is the set unit of music based on established number of beats and isolated by lines on either side of it.
As the first noun in the series, the interpretation is even muddier. A bar tap is the running bill incurred by revellers at a pub and kept by the bartender. However, a barbell (as compared to a bar belle) is a metal object intentionally raised by weight lifters and runners to improve strength. What is not obvious is that a bar fly is not what happens when gym rats get violently drunk or a pesky insect disturbing them but instead someone who contributes to the financial health of several drinking establishments on a regular basis. For that matter, a barcode is the printed computer code on all products allowing price scanning, not the rules of behaviour at a pub. Likewise, a bar chart generally has nothing to do with drinking patterns but instead is a visual representation of data.
So, foreign learners, who represent the majority of English speakers, find themselves at a loss when faced with such a lack of consistency. Keeping in mind Ziva of NCIS fame, native speakers should be tolerant of any errors or misunderstandings they may make in applying even the simplest of words. After all, English is a barry confusing language.