system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Spirits

What is the difference between popular spirits such as whiskey, scotch, bourbon, and rum?

Also when a scotch or whiskey is 'single malt', what does this mean?
gpt
There are a few basic differences.  To make a spirit in the first place, you have to start with a base product.  This can be a grain, as is the case with whiskey, or can be a fruit, such as grapes in brandy, or can be molasses from sugar cane, such as in the case of rum.  Where you are in the world is likely going to dictate what base product you would use to make your booze.
The next thing to consider is the type of still you're using for distillation.  Some people like to use traditional copper pot stills, which give spirits kike Scotch or Bourbon a nice heavy, rich flavor.  Other people, like vodka producers or Canadian whisky makers, like to use special column stills that specifically strip out as much flavor as possible, leaving only ethanol.
The last major thing to take into account with spirits is the aging process.  Many spirits are put into barrels to take on rich flavors over time.  If this barrel is brand new and heavily charred on the inside, it will affect the distillate differently than a barrel that has previously been used for aging something else, like Sherry.
Where the barrel is aged also affects flavor.  A barrel will age more aggressively in a climate that changes from extreme hot to extreme cold, like Kentucky.  Scotland is more moderate in temperature, so barrels there age more gracefully over long periods of time.

"Single Malt"  simply means that all the whiskey in your bottle came from the distillery on the label, vs. a blended Scotch, which could come from multiple distilleries in Scotland.