pedantically, talking to the database will involve sending a request or some kind of IPC, all of which are usually considered side effects.

[handwavy analogy alert]

people often call it "side-effects" as a shorthand. in reality an expression being of type `IO Foo` mostly just tells the compiler that order of execution matters (which isn't the case with pure functions):

  do print "a"
     print "b"
 
  -- obviously not the same as
  
  do print "b"
     print "a"

and also that it can't eliminate common expressions:

  do a <- readBytes file 100
     b <- readBytes file 100
     doStuff a b

  -- obviously not the same as

  do x <- readBytes file 100
     doStuff x x

it's a way of enforcing ordering in a lazy language where evaluation order isn't really defined.