The noun 歌 (gē) means "song" and is one of the most common words for referring to a musical song in Chinese. It appears in many compound words such as 歌手 (singer), 歌曲 (song/melody), and 唱歌 (to sing), and is used in both casual and formal contexts.
她唱的歌特别好听。
tā chàng de gē tèbié hǎotīng.
The songs she sings sound especially beautiful.
这个歌手出了一首新歌,你听了吗?
zhège gēshǒu chū le yī shǒu xīn gē, nǐ tīng le ma?
That singer released a new song — have you listened to it?
他心情好的时候总喜欢哼歌。
tā xīnqíng hǎo de shíhòu zǒng xǐhuān hēng gē.
He always likes to hum a song when he's in a good mood.