This is from the interesting site that Slohairt posted a link to http://www.scots-online.org/grammar/lang.htm

It's long, but worth it.

Language or Dialect?
Popular culture usually thinks of a dialect as a substandard, low status, often rustic form of a language, usually associated with the peasantry, the working class or other parts of the community lacking in prestige. Dialects often being thought of as being some kind of erroneous deviation from the norm - an aberration of the 'proper' or standard form of language.

The fact is that all speakers of any language are all speakers of at least one dialect - standard English for example is as much an English dialect as is any other form of English. No dialect is in any way linguistically superior to any other.

Linguistically speaking dialects are usually regarded as dialects of a language, that is, subdivisions of a particular language

What is a language?

"A language is a collection of mutually intelligible dialects" - A definition which conveniently characterises a dialect as a subpart of a language, and provides a criterion for distinguishing between one language and another.

Another criterion for distinguishing languages from dialects is the Ausbausprache - Abstandsprache - Dachsprache framework developed by the linguist Heinz Kloss. Under the terms of that framework Kloss considered Scots to be a Halbsprache (half language). Ausbau referring to a variety having its own standardized form which is used autonomously with respect to other related languages. The Abstand refers to the distance between the languages as regards mutual intelligibility. A Dachsprache is usually a standard language which 'roofs' different dialects in a dialect continuum.

Take for example, the Scandinavian languages, Norwegian, Swedish and Danish. These are usually assumed to be different languages. Speakers of these three languages can, with little effort, understand and communicate with one another. These languages have little Abstand and are mutually intelligible.
Take for example German, assumed to be a single language. There are varieties of German which are not understood by speakers of other varieties.

What does the above prove? One thing for certain - 'language' is not a particularly linguistic notion at all. The reason why Norwegian, Swedish, Danish and German are thought of as single languages has as much to do with political, geographical, historical, sociological and cultural reasons, as with linguistic ones.

There for the term 'language' is relatively 'unscientific'. Linguists usually refer to 'varieties of language'. There for Norwegian Swedish and Danish could be referred to as varieties of Scandinavian.

Accents
Accent refers to a variety which is phonetically or phonologically (pronunciation) different from other varieties.

Dialects
A dialects is a variety which is grammatically (and perhaps lexically different) as well as phonologically different from other varieties.

Dialects and accents frequently merge into each other without any discrete break.

Geographic Dialect Continua
A dialect continuum is a chain of mutual intelligibility across geographical space. Adjacent dialects are usually intelligible but dialects which are further apart may not be mutually intelligible.

An example of such a dialect continuum is the Romance dialect continuum stretching across the Iberian peninsula through France and parts of Belgium down to the southern tip of Italy. From one place to another across this area there would be some linguistic differences distinguishing one place from the another. Some times the differences would be greater some times less, but with distance they would be cumulative. The further apart the places the greater the differences would become. As the distance increases between places communication becomes increasingly more difficult and eventually impossible. In places far apart the 'dialects' spoken are mutually unintelligible, though all across the dialect continuum a chain of mutual intelligibility exists.

In this example the continuum includes Portuguese, Spanish, Catalan, French and Italian. Where did one language end and the other begin?

Europe has many other dialect continua. The west Germanic language continuum includes Frisian, Dutch (Flemish), Low Saxon, German and Swiss German. The varieties spoken in Ostend in Belgium and Zürich in Switzerland are not mutually intelligible but are linked by a dialect continuum. Low Saxon is often regarded as a dialect of Dutch in the Netherlands and a dialect of German in Germany. The same 'language' a dialect of two different ones? Low Saxon is in fact a marginalised language not a dialect of either Dutch or German.

Another dialect continuum is the north Slavic dialect continuum including Czech, Slovak, Polish, Ukrainian and Russian

As elsewhere in Europe a language continuum exists in the British Isles. Stretching from Cornwall to Shetland. Beat Glauser's research into the Scots / English linguistic border showed that the phonological an lexical borders where almost identical. One of the most marked borders in a European language continuum. This of course has to do with historical and social factors. Before the union of 1707 people in Scotland looked to court Scots as their linguistic standard whereas in England people looked to London. After the Union people in Scotland continued using Scots as an expression of their identity. To a large extent it seems as if English stops at the border and Scots Begins.

Many Scots who speak English do so with a Scottish accent. Their grammar and lexis is standard English, sometimes with traces of Scots grammar and lexis. This is obviously a dialect of English - usually called Scottish Standard English.