This is the 454th most frequent Romanian word.
acel
The Romanian word "acel" means "that" in English.
'Acel' functions as a demonstrative pronoun modifying 'om' to indicate a specific man being referred to.
Acel om este foarte amabil.
That man is very kind.
'Acel' is used here to specify a particular moment being recalled, attaching a sense of definiteness to 'moment'.
Mi-am amintit de acel moment din copilărie.
I remembered that moment from childhood.
'Acel' modifies 'cântec' to refer to a specific song that both the speaker and listener are familiar with.