Difference between Scots and Gaelic

From Dianne:
 I've always been a bit confused about what traditional language was that the Scots spoke in the lowlands. I wondered if it was just English with some 'slang' thrown in? When I was living in Scotland most Scots themselves didn't seem to know. I know in the highlands it was Gaelic.
Anyway this site very succinctly explains that Scots was and is an actual language:

What is Scots?
Scots is the collective name for Scottish dialects such as 'Glaswegian', 'Doric', 'Buchan', 'Dundonian', or 'Shetland'. Taken altogether, Scottish dialects are called the Scots language. Sometimes Scots is known by the names 'Scotch', 'broad or braid Scots', 'Doric' and 'Lallans'.

Is Sots and Gaelic different things?

Yes. Scots belongs to the Germanic family of languages (which includes Dutch, German, English and Swedish) and has traditionally been spoken in the southern and eastern parts of Scotland known as the Lowlands.

Gaelic, on the other hand, belongs to the Celtic family of languages (which includes Irish and Welsh). In recent centuries Gaelic has mostly been spoken in the northern and western parts of Scotland.

How is Scots related to English

The English and Scots tongues began from a common origin but evolved along different paths over hundreds of years until they had grown apart.

This explains why, sometimes, some forms and words can be exactly the same in both, why sometimes they are similar but still different - such as English "more/most" but Scots "mair/maist" - and why sometimes they are completely different - such as English "cry/disgust" but Scots "greet/scunner."

English and Scots are, therefore, sister languages, in much the same way as other closely related pairings, such as Danish and Norwegian, Dutch and German, Irish and Scottish Gaelic, or Spanish and Portuguese.

the links are here:
http://www.ayecan.com/faq.html#answer1

Aye Can - Frequently asked questions - Scottish Census 2011
Scots is the collective name for Scottish dialects such as 'Glaswegian', 'Doric', 'Buchan', 'Dundonian', or 'Shetland'. Taken altogether, Scottish dialects are called the Scots language.
www.ayecan.com