This is the 922nd most frequent German word.
desto
"The more" (used in comparative constructions).
Desto is used in conjunction with 'Je' to form a correlative comparison, indicating that one thing increases proportionally with another.
Je mehr ich lerne, desto besser verstehe ich.
The more I learn, the better I understand.
Desto reinforces the idea of a proportional change when paired with comparatives, again tied with 'Je'.
Desto älter man wird, desto weiser wird man.
The older one gets, the wiser one becomes.
Desto is part of a causative correlation structure supported by 'Je,' typically following the comparative degree of adjectives.