What is the meaning of 'karai' and how is it applied?
"Concentrating on getting territory, rather than playing for influence."

Pasting in the native speaker sources from the Sensei's answer (put there by Bill Spight I think):
辛い（からい）厚みよりも地をとることを意図すること。
from Weblio's Basic Go Dictionary

厚みより地をとることを目的とすること。
from a different go dictionary

厚みよりも実利（地）を重視していること。
From the katteyomi go dictionary 

Also, if you google for "地に辛い" (ji ni karai, i.e. concentrating on taking territory) you get it described as a style of some players (Wikipedia mentions Hane Naoki, Iiyama Yuta, but also says this style of play is becoming more widespread/dominant recently).