Wiktionary
n. (context idiomatic English) An effort or action having very little overall influence, especially as compared to a huge problem.
Usage examples of "drop in the bucket".
Sometimes they throw a war and kill ten or twenty million people, but it's a drop in the bucket compared to stuff like influenza--which the ECC campaigns against by nagging everyone to wash their hands and cover their mouths when sneezing.
He was certain the price was right, but it could hardly be more than a drop in the bucket compared to the estate she must have inherited from Rockwell.
In fact, it was just over five times Spenser's income last year--but it was a drop in the bucket compared to the money he was about to collect for selling it again.
Tomkin, can see that would hardly be a drop in the bucket in solving your country's massive trade deficit.