Meaning of “sag” - Learner’s Dictionary

sag

verb [ I ] uk us /sæɡ/ (present participle sagging, past tense and past participle sagged)
SINK

to sink or bend down:

Our mattress sags in the middle.
BECOME WEAKER informal

to become weaker or less successful:

a sagging economy

(Definition of “sag” from the Cambridge Learner’s Dictionary © Cambridge University Press)