Meaning of “lag behind (sb/sth)” - Learner’s Dictionary

lag behind (sb/sth)

phrasal verb with lag uk us /læɡ/ verb (present participle lagging, past tense and past participle lagged)
MOVE SLOWLY

to move more slowly than someone or something else so that you are behind them

ACHIEVE LESS

to achieve less than someone or something else:

Britain is lagging far behind the rest of Europe on this issue.

(Definition of “lag behind (sb/sth)” from the Cambridge Learner’s Dictionary © Cambridge University Press)