Feeling heavy, sluggish, or listless (physically tired, limbs or body feeling heavy and hard to move).
昨夜はあまり寝られなくて、今日は体がだるい。
I didn't sleep well last night, so my body feels sluggish today.
風邪を引いてから肩がだるくて困っている。
Since catching a cold my shoulders have felt heavy and it's troublesome.
長時間同じ姿勢でいたら足がだるくなった。
After sitting in the same position for a long time my legs felt heavy.
Colloquial/slang sense meaning something is bothersome or a pain to do (close to 'annoying' or 'a pain').
宿題やるのだるいなあ。あとでやろう。
Ugh, doing homework is such a pain. I'll do it later.
朝早く起きるのがだるいから、今日のジョギングはやめた。
I was too lazy to get up early, so I skipped today's jog.
説明を書くのだるいから、口頭で済ませよう。
Writing an explanation is a hassle, so let's do it verbally.