What's in a name?
Whisky Definitions

"Yesterday I had a beautiful dram of a Scottish single malt, from a single cask, on cask strength, with a beautiful finish on a Oloroso cask."
Did you spot the mistake there? Do you, like me, often get lost in all the terminology and rules regarding Scotch whisky?
I tried to help myself with a clear and guiding overview. Maybe it can help you as well?
Let me know if you miss anything after reading on all the terminology below!
(Disclaimer: This article will be focusing on Scottish whisky.)

Single Malt Scotch whisky

Let me start with the most important one for me. It is half my name, so it had the highest priority in my opinion.
The definition of a Single Malt Scotch Whisky is a whisky distilled at  a single Scotch distillery by batch distillation in copper pot stills.
The only ingredients allowed are water, malted barley and yeast. (And later in the process the possible addition of E150. A food coloring.)
The single malt must be bottled in Scotland.
Now some extra details:
Single malt whisky is not the whisky from one batch. If, for example, the bottle says it is a 12 yo whisky, this means that the youngest whisky in the bottle is 12 years old. To get the same flavor in each bottle, the distilleries master blender constructs de whisky out of several "vintages" of whisky to get the flavor just right. So the youngest is 12 years old, the oldest might be a very old whisky! 

Single Grain Scotch Whisky

Next item on the list is something most people are not aware of:
Single Grain Scotch whisky. These whiskies are not always available at your local liquor store, but there are many different kinds available.
Opposite of what you might expect since you just read the definition of a Single Malt whisky, is that the single in Single grain is just referring to the one distillery. It can contain a combination of malted or unmalted grains or cereals. Another factor that is often mentioned is that a large amount of grain whiskies are distilled in column or patented stills. However, this is not required. (The other way around might count: A 100% malted barley whisky can not be a single malt, but can be a grain whisky. Due to the required copper pot stills.)
So the definition of a Single Grain Scotch Whisky would be a whisky, distilled out of water, yeast and a combination of (malted) grains or cereals,  being produced at one distillery. 

Blended Scotch Whisky

Being by far the biggest exported kind of whisky from Scotland, Blended Whisky needs to be defined as well.
The definition is in the name: Blended Scotch Whisky, is a whisky consisting of one or more single malt whiskies and one or more single grain whiskies.
So the ingredients are in this case the end products of the first two whiskies as described above. The master blender has a large amount of ingredients to choose from, but at the same time has to make sure every batch is similar to the previous batches. Some of the biggest brands that are known all across the globe are blends. Think, for example, about that one guy that is always walking.
But wait, there's more!

Two extra kind of blended whisky

Next to the "normal" blended scotch whisky, we have two sub-categories that I need to mention:

Pretty clear now I hope? I will add one final entry that  I hope will not lead to a whole new thread of information:

Single Cask Whisky

Now this is a special one: Single Cask Whisky is like the name suggests:
A whisky bottled from one cask. Often this whisky is also bottled at cask strenght, which means it is not diluted with water before bottling.
Opposed to the other definitions on this page, this naming is not ruled by the Scotch  Whisky Regulations. But lets make it confusing:
What if the whisky is labled double cask or is finished on another cask?
Difficult and vague. But according to this article I found, double barrel whisky can be single cask, IF the cask is the same type as the first one. So that would mean a whisky with a finish is not allowed to be called a single cask whisky.
However, according to the EWA this  is not the case:
"While not specifically defined in the Scotch Whisky Regulations (2009 UK legislation outlining legal requirements for Scotch), the term falls under the Consumer Rights Act (2015 UK legislation outlining general consumer protection) which states that any food description must be accurate, clear and not misleading." and "The term “single cask” should only be used when the contents of the bottle have spent the entire maturation period in a single cask."

To be honest, I'm confused again.