Teleport: Character disappears, magically reappears moments later in a different spot.
Dash: Character moves so quickly that it looks like he's teleporting.
The end result is the same, but there are a few pretty important implications if it's supposed to be one or the other, all revolving around whether or not the character's body is actually passing through point B on his trip from A to C. For example, if there's a mine or tripwire between his starting and ending position, does he pass through or trigger it? Or if the starting and ending points are both hidden, but the path moves him out of cover and directly in enemy line of sight, do the guards notice something zip by?
The reason I'm asking is because when I played Mark of the Ninja, I had an unnecessary amount of difficulty getting past certain obstacles because I didn't realize that the "dash" move you can get later on actually lets you safely travel through lasers and enemy line of sight.