adverb [ADV prep] Smack dab is used in expressions such as 'smack dab in the middle' of somewhere to mean exactly in that place. [mainly US, informal]regional note: in BRIT, also use slap bang. ...an old brick building smack dab in the middle of downtown.

Is smack dab informal?

adv. Informal. directly; squarely.

Where does the phrase smack dab come from?

"make a sharp noise with the lips," 1550s, probably of imitative origin (see smack (v. 2)). With adverbial force, "suddenly, directly," from 1782; extended form smack-dab is attested from 1892, American English colloquial (slap-dab is from 1886).