Bangs-and-Smells Magic – Harry Potter Lexicon

"Many witches and wizards, talented though they are in the area of loud bangs and smells and sudden disappearings, are yet unable to penetrate the veiled mysteries of the future."
-- Sibyll Trelawney (PA6)

Bangs-and-Smells Magic is a general term for the kind of overt, showy magic which may be considered by some to lack subtlety.

References from the canon

Snape's makes a similar reference in his comment regarding the subtlety of potion-making: "As there is little foolish wand-waving here, many of you will hardly believe this is magic" (PS8).
Gilderoy Lockhart displayed Bangs-and-Smells Magic when he shot a snake high into the air during the Duelling Club: "He brandished his wand at the snake and there was a loud bang; the snake, instead of vanishing, flew ten feet into the air and fell back to the floor with a loud smack." (CS11).
Divination is totally different from loud and showy magic (PA6).
Hermione said the Weasley Twins "only know flashy stuff that's of no real use to anyone" but later had to express her admiration for their fireworks that disrupted all the classes at Hogwarts and drove Umbridge crazy (OP17, OP28).
As Harry watched Dumbledore quietly searching by touch for a way into the Sea Cave hidden by Voldemort, he realized he had "long since learned that bangs and smoke were more often the marks of ineptitude than expertise" (HBP26).
According to Mr. Ollivander, acacia wand wood "is not suited to what is commonly known as 'bangs-and-smells' magic." (Pm)