This is the 723rd most frequent Italian word.
d
The Italian word "d'" is a contraction of "di," meaning "of" or "from."
The 'd' in 'di Maria' indicates possession—'the house belonging to Maria'
La casa di Maria è grande.
Maria's house is big.
The 'd' in 'd'acqua' connects the noun 'bicchiere' to the content it holds, 'water'
Un bicchiere d'acqua, per favore.
A glass of water, please.
The 'd' in 'd'improvvisare' links the noun 'arte' to what it pertains to—'improvising'.