Zer means under/weak/defeated
Zer is also a vowel in urdu which is used below letters to indicate the sound of i.
Usually it is used in conjunction with other words, examples are given below:
zer-e-lab– in a whisper/under ones lip
zer-e-aab– under water/submerged
Given below is a beautiful Couplet by poet Majaz which uses the word zer-e-lab.
Phir chalili hai rel isteshan se laharaati hui,
neemshab khaamoshi mein zer-e-lab gaati hui
meanings : isteshan- station, neemshab- midnight, zer-e-lab-wishpering
Zer-e-lab is also the title of a book which is a collection of letters written by Safiya Akhtar to her husband poet Jan Nisar Akhtar.