Lush describes something growing in abundance, like the lush green grass that covers the lawn in the spring.
Lush usually describes thick healthy plant growth, like the jungles of the rainforest that were so lush you couldn't walk through without chopping down branches. (Then it wasn't so lush anymore...oops!) Lush also means "plush" or even "extravagant" — like a thick shag carpet, music with lots of layers, or a bedroom wallpapered in velvet. Plants full of juice are lush, which is perhaps why a person who drinks too much alcohol is called a lush.