I'm sure you have heard the two separate terms "language" and "dialect." You may have wondered what the heck the difference is between the meanings of the two words. I am here to clear things up a bit for you.
Linguists have a tough time clearly defining the difference between the two terms, but I will give you some loose guidelines on distinguishing between a language and a dialect.
The definition of this difference is made a little easier by means of a little thing called "mutual intelligibility." If two forms of speech are mutually intelligible, this means that speakers of both varieties can understand one another. If mutual intelligibility exists between two types of speech, they can usually be considered dialects of the same language. For example, I can understand an Englishman quite well. This is because American English and British English are dialects of the same language. But when two people do not understand each other's speech at all, they most likely speak two separate languages. I cannot understand a German speaker. Even though German is in the same language family as English (more on language families later), it is not a dialect of English. It is a totally separate language.
Some exceptions to this rule exist, complicating our tidy little definition.
Sometimes a language is defined by political or cultural boundaries. One example is that of the Swedish, Norwegian, and Danish languages. The three languages are practically mutually intelligible. Speakers of Danish can understand most of what speakers of the other two languages are saying. So these three are all be considered dialects of the same language, right? Nope. Because of political boundaries (they are the dominant languages of three different countries), they are all considered different languages. This is also a case of national identity (a Swede would rather say "I speak Swedish" than "I speak the Swedish variety of Scandinavian"). Here are some more examples of separate languages that we should (arguably) consider dialects of the same language:
This also works in reverse. I have found some instances in which, due to their very unique vocabularies, dialects should perhaps count as a totally separate languages instead. Here are some examples:
Hassaniya Arabic (spoken in Mauritania)
Moroccan Arabic (Morocco)
Pitcairn English, also called Pitkern (Pitcairn Islands)
I know there are other good examples out there; but those are the ones I could name off the top of my head.
So I hope this helps you to understand exactly (or remotely) what a dialect is, versus what a language is. That is the first thing you should take from this. But the second most useful bit in here is this: If you want to learn Arabic for a trip to Egypt, don't learn it from a Mauritanian -- they speak Hassaniya, not Arabic.