This is the 37th most frequent Romanian word.
cei
"The ones" or "those" (used as a demonstrative or pronoun).
'Cei' functions as a relative pronoun, referring to 'those' in English, and it is connected to the clause it introduces.
Cei care au participat la întâlnire au primit un cadou.
Those who attended the meeting received a gift.
'Cei' specifies or points out a particular group, in this case 'the two', and indicates a determiner role in the sentence.
Într-un colț, stăteau cei doi prieteni ai mei.
In a corner, my two friends were sitting.
'Cei' operates as part of a comparative structure 'cei mai buni', meaning 'the best', thus helping form a superlative phrase.