This is the 19th most frequent French word.
aux
"Aux" is the contraction of "à" (to, at) and "les" (the) in French, meaning "to the" or "at the."
"Aux" is used to combine "à" (to) and "les" (the plural definite article) to indicate movement towards a plural place.
Ils sont allés aux montagnes pour faire une randonnée.
They went to the mountains for a hike.
"Aux" combines "à" (to) and "les" (the plural definite article) to indicate the indirect object of the action expressed by a plural.
Elle a donné des cadeaux aux enfants.
She gave presents to the children.
"Aux" combines "à" (to) and "les" (the plural definite article) to indicate an activity or location expressed as a plural noun.