This is the 22nd most frequent Italian word.
alle
"Alle" is the contraction of "a" (to/at) and "le" (the, feminine plural).
Here, 'alle' means 'to the', where 'a' (to) is combined with 'le' (the plural feminine article) specifying a movement towards a plural feminine noun.
Andiamo alle montagne.
We are going to the mountains.
In this sentence, 'alle' refers to a specific time, particularly indicating 'at a certain hour' by combining 'a' (to/at) with 'le' (the plural feminine article referring to the hours).
Ci vediamo alle tre.
We will meet at three o'clock.
In this example, 'alle' is part of the prepositional phrase 'alle quali,' meaning 'to which,' and it establishes a relative clause providing additional information about the subject. It is the combination of 'a' (to) with 'le' (the plural feminine article) used with 'quali' (which) as a plural feminine relative pronoun.