Why do we not use the definite article in "Where can I find the room 401?"

Last week in college, a student [with a thick South Asian accent] asked me:

"Excuse me, where can I find the room 401?".

I realized that to my native English ears, the word "the" sounded non-native. This had me realize that we sometimes use no article.

I am learning French; in French, we seem to always use some kind of article before nouns. It surprised me, at that moment, to realize that English doesn't always do the same! (That, and using the definite article in "the room 401" seems to make sense if I think about when definite articles are used).

Is there a grammatical name or concept for this "no article" aspect of our language? Are there any websites that can explain this to me?

Answer

This answer addresses the two questions at the bottom of the body of your question, but only tentatively addresses the question in your title.

The grammatical construct where the article is missing appears to be called the zero article. There is also a book written about the zero article.

One might have thought that zero articles are used when the noun is inherently unique, since there is no need then for an article to distinguish any one of many from a specific one of many. However, English is inconsistent here. One example that has come up in a similar discussion is The Eiffel Tower. Another example (from the book, IIRC) is The Baltic Sea. In both cases, the noun is unique but the definite article is part of its name.

One suggestion is that we always use the zero article with names. In examples such as The Eiffel Tower and The Baltic Sea, the word The is considered to be part of the name rather than a separate article. Street names are similar. For example, "Where is Main Street?" has no article but "Where is The Strand?" does because The is part of the name The Strand. Note that this doesn't cover all cases since "I can design an Eiffel Tower" and "I can pave a Strand" are arguably acceptable. In many cases, though, this 'rule' holds.

In the case of your question, Room 401 is the name of the location, but the location is not so grand as to warrant having "The" as part of its name. The definite article is therefore not used before Room 401 in the sentence in your question's title.