The highest score obtainable in Pac-Man

The Character (Personality), nicknames and behavior for the enemies are:

• Red: Shadow "Blinky" In Japan, his character is represented by the word oikake, which means “to run down or pursue”. (Chases Pac-Man all the time, Also speeds up after you've eaten a certain amount of dots, which gets less for each level.)

• Pink: Speedy "Pinky" In Japan, he is characterized as machibuse, meaning “to perform an ambush”. (Fast but random movement.)

• Cyan: Bashful "Inky" In Japan, he is portrayed as kimagure, meaning “a fickle, moody, or uneven temper”. (Shy and tries to stay away from pac-man, unless approached too much, after which it will chase Pac-Man too.)

• Orange: Pokey "Clyde" In Japan, his character is described as otoboke, meaning “pretending ignorance”, and his nickname is “Guzuta”, meaning “one who lags behind”. (Slow and Random Movement)

Now, on the ghost vs. monster topic, The arcade cabinet refered to the enemies as "monsters", but the when the Atari 2600 home version was released with pale, flickering enemies, the manual dubbed them "ghosts", to add to the confusion, the TV series refers to them as "ghost monsters" (I personally prefer ghosts.)

Source for the behaviours:

• Mateas, Michael (2003). "Expressive AI: Games and Artificial Intelligence" (PDF). Proceedings of Level Up: Digital Games Research Conference, Utrecht, Netherlands.
• Pittman, Jamey (2011), The Pac-Man Dossier

Sparks happen when you are trying to turn, but can't. That is, when you're pushing into a wall. This also has the side effect of making you turn faster when the turn becomes possible. So if you plan ahead and "spark into" your turns, you'll corner faster than if you had waited until the actual intersection to change your direction.